Google Shopping CSS: how the system works and why your bid counts in full

What is a Google Shopping CSS?

CSS stands for Comparison Shopping Services – price comparison services – and it applies to the results on Google's main search page.

Price comparison portals (CSSs) can bid to place Shopping ads for the merchants they represent on Google's search results pages. Google Shopping bids on behalf of the merchants it represents in the same way as any other price comparison portal.

This means that as a merchant, you can use the Shopping ads on the Google search results page in different ways. You can submit your product data to any price comparison portal, including Google Shopping. But you can also use several price comparison portals in parallel.

Originally, Google used the search results page exclusively for its own price comparison service, Google Shopping. Other price comparison services only appeared much later. In 2017 the EU Commission fined Google €2.42 billion for unfair competition, because Google had used its near-monopoly market position to favour its own offer.

To create a level playing field, Google rebuilt its advertising platform as a price comparison service under the name Google Shopping Europe (GSE) and opened it up to external price comparison sites – the so-called Google CSS partners. As a result, every Shopping ad in Google's main search is part of a comparison shopping service (CSS).

Google Shopping itself also appears as a CSS ("By Google"), takes part in the bidding auction just like the other price comparison platforms, and competes with the other CSSs that bid on behalf of merchants.

So that Google can run its own price comparison service in line with EU rules, it keeps 20% of the bid of every merchant who uses Google's own price comparison service. This is the only way Google Shopping Europe can count as an independent price comparison service, which therefore has to operate at a profit.

However, this lowers the bids of every advertiser using Google Shopping Europe by 20%. If you use a CSS partner for your ads, that margin disappears entirely.

For Google users the difference is barely visible – the only visible change is the "By …" line at the bottom of the ad.

With a Google CSS, your full bid enters the auction

As an advertiser, the main thing that changes for you is how much of your Google Shopping bid goes into the Ad Rank auction:

Say you start with a CPC bid of £1. If you still use Google Shopping Europe, £0.20 is deducted. The result: you compete for Ad Rank with a reduced bid of £0.80.

If you advertise your products through a Google CSS partner instead of GSE, that margin disappears. Your bids enter the auction in full – the whole £1.

Your advantage: with the same budget, you bid with 25% more bidding power. If you hold your position instead, you save 20% CPC.

Google Shopping CSS pays off for everyone who runs Shopping ads

If you run Google Shopping Ads without your own CSS, your bids are reduced. The switch changes nothing in your campaigns, only how much of your bid reaches the auction.

Every competitor already bidding through a CSS partner enters the auction with their full bid. Without your own CSS, you only bid an effective 80p per pound – and that shows in exactly the positions where you compete against them.

Advertisers using GSE pay 20% more per click for the same position than they would through a CSS partner. CSS providers usually charge a fixed monthly fee for their services, sometimes a share of media spend.

In most cases, the cost of using an external CSS is lower than GSE's margin.

Google CSS alone or alongside Google Shopping: two strategies compared

Once you have decided to switch to a Google CSS partner, the question is the best account and campaign setup: should all accounts move to a CSS partner, or are there advantages to splitting accounts between GSE and CSS?

Option 1 – dual strategy: you use Google CSS and Google Shopping Europe in parallel and serve traffic with different bids depending on placement (Google's main search vs. the Google Shopping tab and partner networks). High bids on the main page through a CSS account, low bids on the Shopping tab and in partner networks through a GSE account. Especially relevant for very large advertisers who don't mind the extra work.

Option 2 – switching entirely to CSS: in practice, the dual strategy rarely delivers measurable added value, while the maintenance effort is considerably higher. We therefore recommend moving all accounts and Google Shopping campaigns to CSS – very little effort, full use of every CSS advantage.

Connecting a Google CSS in Merchant Center: full switch or association

To serve Google Shopping ads through a CSS partner, there are two ways to move an existing Google Shopping Europe account to CSS: full switch or association.

With a full switch, the advertiser's Merchant Center Account (MCA) is fully integrated into the CSS partner's Multi Client Merchant Center (MCC). There are a few technical points to bear in mind. If only a sub-account is moved rather than the entire MCA, access rights can be lost during the move.

The main advantage of a full switch: the CSS partner has access to the product data and can spot and fix problems directly. In return, you depend more on the CSS partner than with the association model, which requires trust.

If you choose the association model, your MCA is linked to the CSS partner in a relatively simple way. Your setup stays unchanged: the CSS partner sends a link request and you confirm it in your Merchant Center. If only a sub-account of an MCA is switched, the same access-rights risks apply as with a full switch.

The advantages of a full switch (full access to the product data for the CSS partner) do not apply directly here. However, the CSS partner can be given access to the client account or the data feed via a user invitation.

A full switch and an association barely differ in handling and collaboration. Whether you move your entire account into the CSS partner's MCC or connect it via association is more a question of trust, control and flexibility.