Advertising with CSS: how a Comparison Shopping Service cuts your Google Shopping costs

The real decision

The real question isn't: should I use a CSS? It's: should Google Shopping represent my products, or an independent CSS Partner?

An independent Google CSS Partner can represent your products in Shopping ads and free product listings. Depending on the provider, you keep full control over Google Ads and Merchant Center, or hand feed and campaign management over to the CSS in part or entirely. Google distinguishes between managed-service, self-service and hybrid models for this.

A CSS is therefore not an additional advertising channel alongside Google Shopping. It's the entity through which your product data and Shopping ads are served on Google in the supported markets.

The essentials of advertising with CSS at a glance

• CSS stands for Comparison Shopping Service.
• Google Shopping is itself a CSS. You can choose an independent CSS Partner instead.
• Your Shopping ad still leads directly to your online shop.
• In the ad, mainly the "By" line changes, showing the name of the responsible CSS.
• Your existing Google Ads campaigns can, in many cases, stay in place when you switch accounts.
• A Merchant Center account can only ever be linked to one CSS at a time.
• You can generally work with several CSSs at the same time, but you need the right account structures for it.
• For free product listings in Europe, you can only select one CSS.
• CSS also works with automatic bid strategies and feed-based Performance Max campaigns.
• The CSS advantage: 20% lower CPC at the same position, or 25% more bidding power at the same budget.

What is a Comparison Shopping Service?

A Comparison Shopping Service collects product offers from various merchants and lets users compare products, prices and offer conditions with one another.

For Google Shopping, the CSS takes on a second role: it can represent merchants to Google and place their products in Shopping ads or free product listings.

The CSS is the price comparison service that represents your shop in the CSS programme. That can be Google Shopping or an independent provider such as csspartner.io. Your product data is managed in the Google Merchant Center, including:

• Product ID
• Product title
• Description
• Price
• Availability
• Image
• Brand
• GTIN
• Product URL
• Shipping information

Merchant Center decides on the basic eligibility of your products and supplies the data for Shopping ads and free product listings.

In Google Ads, you manage campaigns, budgets, bid strategies, target values and reporting. Depending on the service model chosen, either you, your agency or the CSS works in this account.

So the CSS doesn't replace Merchant Center or Google Ads. It adds to the account structure as the responsible price comparison service.

Why does the CSS programme exist?

The origin of the CSS programme lies in European competition law. In 2017, the European Commission imposed a fine of €2.42 billion on Google. In the Commission's view, Google had favoured its own price comparison service in search results and disadvantaged competing price comparison services.

Google was then required to create a model in which other price comparison services could take part in the placement of Shopping ads. Since then, Google Shopping has acted as one CSS among several in the affected markets. Merchants can submit their product data to Google Shopping or to an independent Comparison Shopping Service.

That's also why the line under a Shopping ad doesn't always read "By Google", but for example "By csspartner.io" or the name of another price comparison service.

How does advertising through a CSS work?

The process breaks down into six steps.

1. Your product data is supplied in Merchant Center – from your shop system, an XML or CSV file, a feed management solution, a direct API connection or an automated website data source. This data determines which products and search queries your ads are eligible for.

2. Merchant Center is linked to a CSS. When switching, an existing account can be transferred from one CSS to another. The new CSS initiates the switch; an administrator of the Merchant Center account confirms or declines it.

3. Merchant Center is linked to Google Ads. Through this connection, the product data can be used in Shopping or Performance Max campaigns. A CSS switch doesn't automatically mean you have to switch your existing Google Ads account.

4. Your products take part in the ad auction. Google checks, among other things, product relevance, product data, bid or bid strategy, expected ad quality, competition, user context, and campaign and budget settings. The chosen CSS submits the bid for the merchant it represents into the auction.

5. The Shopping ad is served – typically with a product image, product title, price, shop name, possibly ratings and the name of the CSS. Clicking the CSS attribution leads to the price comparison service's website.

6. Clicking the product leads to your shop. A normal click on the Shopping ad doesn't first go to the CSS's website, but directly to the merchant's product page. All CSSs and merchants are subject to the same basic Shopping policies and requirements for product data and landing pages.

What changes with an independent CSS Partner?

A switch changes less than many merchants initially expect.

How big the operational change turns out to be depends on the service model. With a lean self-service setup, the change can be limited essentially to the CSS assignment. With a full-service model, the provider can instead take over Merchant Center, feed, Google Ads and campaign management entirely.

The CSS programme is growing into more countries

The 21 active CSS markets aren't only EU states: Switzerland, Norway and the United Kingdom are included too, and the CSS advantage applies there just the same.

According to its own country launch announcements, Google is expanding the programme to Bulgaria, Croatia, Estonia, Latvia, Lithuania, Luxembourg and Serbia from September 2026, and to Slovenia from March 2027.

From each respective launch, the same advantage applies: 20% CPC savings or 25% more bidding power.

Without a CSS, Google Shopping keeps a markup on every click

Without your own CSS, Google Shopping serves your ads itself and keeps a markup on every click. Through an independent CSS such as csspartner.io, that markup disappears, and your full bid goes into the auction.

Here's how the difference works out:

If you hold your position, you save 20% CPC. If you keep your budget the same, you bid with 25% more power – because £1 is a quarter more than 80p.

Three strategies after switching to a CSS Partner

Strategy 1: grow reach and revenue. You leave budgets, bids and target values unchanged for now. Thanks to the higher effective auction bid, your products can become competitive in more auctions – possible results include more impressions, a higher share of possible impressions, more clicks, higher conversion volume and more revenue. This strategy suits campaigns that are already profitable.

Strategy 2: improve efficiency and profitability. You gradually reduce your bids or tighten your efficiency targets. With manual CPC bids, a reduction can be tested directly. With target ROAS, maximise conversion value or Performance Max, you should proceed more cautiously – an abrupt change can affect the campaign more than the CSS switch itself. Watch average CPC, cost per conversion, conversion value, ROAS, impression share and lost impression share.

Strategy 3: measure the effect in a controlled way. For most merchants, this is the most sensible approach. Keep the key campaign settings stable at first and document how things develop. Don't change CSS, product feed, target ROAS, budget and campaign structure at the same time – otherwise it's hard to tell which change was responsible for the result.

Full service, self-service or hybrid?

CSS Partners can offer very different levels of service. Google distinguishes three basic models.

In the full-service model, the CSS often creates or manages Merchant Center, the Google Ads account, the product feed, campaigns, bids and reporting. Billing can take the form of a monthly agency fee, a fixed cost per click, a percentage of ad spend, a revenue share or performance-based commission. The advantage lies in low internal effort, the downside in stronger dependence on the provider. So check carefully who owns the accounts.

In the self-service model, you manage product data and campaigns yourself, or through your existing agency. The CSS mainly handles CSS assignment, setup, migration, technical support and, where relevant, additional reports or tools. You shouldn't pay for a second campaign agency if your team already handles that task reliably.

The hybrid model splits responsibility: the CSS optimises the feed and you manage the campaigns, or the other way round. The model is flexible but needs clear responsibilities. Put in writing who is responsible for feed errors, rejections, tracking, budgets and campaign changes.

Does a CSS Partner work with Performance Max?

Yes. Feed-based Performance Max campaigns use product data from the Google Merchant Center. If Merchant Center is assigned to a particular CSS, the Shopping activity drawn from it belongs to that CSS. Google generally makes features such as conversion reporting and automatic bid strategies available to all CSSs.

Performance Max is broader than a classic Shopping campaign, though. These campaigns can appear in Google Search, the Shopping tab, Google Images, YouTube, the Display Network, Gmail, Demand Gen and Google Maps, among other places.

The CSS mainly affects the product-related delivery through the connected Merchant Center feed. So you shouldn't automatically attribute every change in overall Performance Max performance to the CSS. Look at product performance separately, check Shopping and Search placements, note changes in channel distribution, and compare conversion value rather than just click prices.

By default, a CSS can place products in the Shopping unit of general Google search results. Some CSSs have additional approvals for further surfaces such as the Shopping tab, YouTube, the Display Network or dynamic remarketing. Before switching, you should check whether the new provider supports the surfaces you need.

How do free product listings work through CSS?

Besides paid Shopping ads, CSSs can also represent products in free product listings. One important restriction applies: for free product listings in Europe, only one CSS can be selected per merchant domain.

This selection is made in the CSS dashboard of Merchant Center. If the CSS selected for free product listings doesn't match the Merchant Center account being used, products can be rejected for this destination.

When switching, you should therefore check not just the paid campaigns, but also the CSS selected for free listings, the products' destination programmes, the approvals in Merchant Center, the country assignment, and any existing diagnostics and rejections.

Can you use several CSSs at the same time?

Yes. Google generally allows merchants to have their products advertised through several CSSs at the same time. However, a Merchant Center account can only be assigned to one CSS at a time. Parallel use therefore relies on different Merchant Center structures, or separate accounts.

Does this mean you end up bidding against yourself? No. Google explains that a merchant isn't second-priced against themselves in the auction. If CSS A submits a bid for your shop and CSS B submits another bid for the same shop, the click price you pay is based on the next-highest bid from a different merchant.

Google also tries to show identical offers of the same product and merchant only once in a Shopping unit. In rare cases, two offers can appear if they aren't reliably recognised as identical. Different products from the same merchant, on the other hand, can certainly be served at the same time through different CSSs.

Parallel use can be worthwhile if different CSSs cover different countries, one provider handles the feed and another the campaigns, or a large organisation separates different brands. For many small and medium-sized merchants, though, a single reliable CSS is easier to manage. A multi-CSS setup should serve a specific goal, not just be set up because it's technically possible.

How can you switch your CSS Partner?

Switching doesn't have to mean rebuilding your campaigns from scratch.

Step 1: review your existing setup. Document your Merchant Center ID, Google Ads account, linked accounts, target countries, product data sources, free product listings, dynamic remarketing, local inventory ads, additional Google surfaces, and current users and access rights.

Step 2: choose a new CSS. Clarify in advance country coverage, service model, price, contract term, support, account access, billing, migration assistance, delivery beyond general search, and how free product listings are handled.

Step 3: initiate the switch. The new CSS initiates the switch of the Merchant Center account. An administrator of Merchant Center then gets the option to approve or decline the change.

Step 4: check the Google Ads connection. The Google Ads account doesn't need to be transferred for a normal CSS switch. Still, check that the Merchant Center link is active, that all campaigns are pulling the right product data, that no products have been unexpectedly excluded, that conversion tracking is still working, and that automatic bid strategies are receiving data.

Step 5: monitor delivery. Check product status, impressions, clicks, cost, average CPC, conversion volume, conversion value, ROAS, free product listings, target countries, and remarketing and other surfaces. Google notes that after a switch, delivery outside general search or in countries outside the CSS programme can drop if the new CSS doesn't support those areas.

What does a CSS Partner cost?

CSS Partners use different pricing models. With a fixed monthly fee, you pay a set amount regardless of your Shopping budget – easy to calculate, and relatively cheaper as your ad budget grows. With a percentage CPC markup, the CSS charges a surcharge on click costs; that looks cheap on small budgets but automatically gets more expensive as your ad spend grows.

With a share of ad spend, the fee is based on the managed Shopping or Google Ads budget – clarify whether the share applies only to Shopping or to all campaign types. With a revenue or performance share, the attribution model, returns, cancellations, tax and shipping costs need to be clearly defined. A full-service package bundles CSS, feed management, Google Ads management and reporting together, making a direct price comparison harder.

Don't rely only on the publicly advertised entry price. Total annual cost = CSS fee + setup + countries + accounts + tools + campaign management + support + internal effort. A free CSS can require a paid agency service or software. What matters isn't whether the CSS line item itself is free, but what the complete solution costs.

How do you find the right CSS Partner?

The auction mechanism is only part of the decision. In practice, providers differ mainly in service, technology, cost and contract terms.

In Google's CSS partner directory you can filter by countries, industries and languages, and also by partners with API feed technology or by Premium Partners that, according to Google, have additional technical certifications and offer conversion tracking for merchants. The status doesn't replace your own comparison.

Ten questions for the provider conversation: what one-off and monthly costs apply? What's included in the price? Which countries is the CSS approved for? Which Google surfaces are supported? Does my existing Merchant Center stay in place? Does my existing Google Ads account stay in place? Who owns the accounts and admin rights? How do cancellation and a later switch work? What support is included? Can agencies offer the service as White Label?

Keep a written record of all the answers. This avoids later misunderstandings about responsibilities or extra costs.

Google's CSS Partner Program recognises CSSs; our agency partner programme is built for agencies

With the CSS Partner Program, Google places Comparison Shopping Services in three tiers: Participant, Partner and Premium Partner. Every CSS that takes part in the programme is a Participant.

A CSS becomes a Partner with at least 50 merchants running active Shopping campaigns and a place in the top 20% of all CSSs in its region by Shopping ad impressions. Premium Partners are in the top 10% and agree an annual partnership plan with Google that includes four quarterly business reviews. Partners and Premium Partners appear in Google's CSS partner directory and carry a badge.

csspartner.io is a Premium Partner. But you get the CSS advantage whatever the tier: any CSS gives you 20% lower CPC at the same position or 25% more bidding power at the same budget.

Our agency partner programme is something different. It is aimed at agencies that connect their clients via csspartner.io: from 3 active clients they pay 15% less for each CSS access, from 6 clients 25% less and from 11 clients 35% less.

How do you measure the success of a CSS switch?

Document a solid baseline before the switch. Record at least impressions, clicks, click-through rate, average CPC, cost, conversions, cost per conversion, conversion value, ROAS, impression share, impressions lost due to ad rank, and the number of active and rejected products. For Performance Max, also check product groups, search categories and available channel information.

Don't compare a normal sales week with Black Friday, Christmas, a sale, a range change, a price increase or a seasonal demand spike. A before-and-after comparison only makes sense if the underlying conditions haven't changed substantially.

Also keep a record of: the date of the CSS switch, budget changes, new target values, feed adjustments, price promotions, range changes, tracking updates, new campaigns and changes to conversion goals. This helps you make sense of later performance differences.

Who benefits from an independent CSS Partner?

A CSS Partner is particularly worthwhile if you're already actively using Google Shopping, run Performance Max with a Merchant Center feed, your Shopping budget is well above the CSS fee, your campaigns are fundamentally profitable, you're looking for extra reach or efficiency, you want to manage your campaigns yourself, you already work with a Google Ads agency, you sell in several European markets, or you're an agency wanting to offer CSS to your clients.

The potential benefit is smaller if you're not yet running Shopping campaigns, your ad budget is very small, your product feed contains many errors, conversion tracking isn't working reliably, your products aren't approved on Google, you advertise exclusively outside the CSS markets, or your shop barely converts purchase-ready traffic.

CSS optimises the auction's underlying terms. It doesn't replace a working e-commerce and campaign strategy.

The CSS name under the ad shows who isn't paying the markup

A Comparison Shopping Service connects your product feed to Shopping delivery in the supported European markets. The choice of partner affects cost, support, account access, country coverage, and the effort involved in setup and switching.

A controlled switch documents the starting performance, keeps campaign settings stable at first, and compares reach, cost and conversion value before and after the change.

Switch to an independent Google CSS with csspartner.io

csspartner.io offers the CSS connection as a flat rate: no setup costs, no click commission and no minimum term. Migration is handled for you, while you keep control of campaigns and budget.

That way you can use the CSS advantage without having to hand your existing Google Ads strategy over to a new campaign manager.