What does CSS mean in Google Shopping?

CSS stands for Comparison Shopping Service: a Google-approved price comparison service through which stores place their Shopping ads in Europe. Google Shopping is Google's own CSS; the others are partner CSSs.

Do I really save 20% on every click?

Up to 20%. Through Google's CSS about 80% of your bid enters the auction; through a partner CSS 100% does. The real saving depends on competition for your products and on your bidding strategy; most accounts see 10–20%.

Do my campaigns stop when I change CSS?

No. The switch is an approval in Merchant Center and does not affect your campaigns, feed or Google Ads history.

Can I use one CSS for several countries?

Yes. A CSS can place ads in any country of the CSS programme (EEA, Switzerland, UK) where it is approved. Bigconvert CSS covers every country in the programme.

Can I go back to Google Shopping or change CSS later?

Yes, at any time, through the same approval in Merchant Center. Your Merchant Center account stays yours.

Does a CSS manage my campaigns?

Not necessarily. A self-service CSS like Bigconvert CSS only places your ads through its domain and has no access to Google Ads. Some agencies bundle the CSS with campaign management.

What is Google CSS and how does it lower your Google Shopping cost per click

If you run Google Shopping ads for an online store in Europe, every click you pay for goes through a Comparison Shopping Service, or CSS. Most stores never chose one: they use Google's own CSS, called simply "Google Shopping". This article explains what a CSS is, why a partner CSS can cut your cost per click by up to 20%, what changes (and what does not) in your account, and how to pick one.

What is a CSS (Comparison Shopping Service)?

A CSS is a price comparison website that Google allows to place Shopping ads (the product cards with image, price and store name at the top of Google results) on behalf of the stores it represents. Every Shopping ad in Europe is placed by a CSS. Under the price you see the label "By Google" when the ad is placed by Google's CSS, or "By [CSS name]" when a partner CSS placed it, for example "By Bigconvert.com".

The programme exists only in Europe: the countries of the European Economic Area, Switzerland and the United Kingdom. There are no CSSs in the United States or Asia, because the legal obligation that created them does not exist there.

Google keeps an official list of approved CSSs, filterable by country and language: the Comparison Shopping Partners directory. Any CSS in the directory has passed Google's checks and is safe to use.

Why CSSs exist: the European Commission decision of 2017

On 27 June 2017 the European Commission fined Google €2.42 billion for favouring its own price comparison service in search results over competing comparison sites. To comply, Google changed how the Shopping carousel works in Europe from September 2017:

Google Shopping became a separate unit that takes part in the ad auction like any other comparison service.
Any price comparison site that meets Google's requirements can become a CSS and place Shopping ads for its stores.
To be profitable as a stand-alone unit, Google Shopping keeps a margin out of the bids of the stores it represents. Partner CSSs have no such obligation.

The whole cost difference, explained below, follows from these three rules.

Save up to 20% on every Google Shopping click

Bigconvert CSS: €18.99 per month per store, no commission, cancel anytime. Activation takes 5 minutes.

Activate Bigconvert CSS

Where the up to 20% lower cost per click comes from

When you bid €1.00 for a click through Google Shopping (Google's CSS), about €0.80 enters the actual auction: the difference is the margin Google Shopping keeps as a comparison service. When you bid the same €1.00 through a partner CSS, the full €1.00 enters the auction.

You see the effect in one of two ways, depending on how you run your campaigns:

What you keep constant	What changes
The same bids	Better positions and more impressions and clicks for the same budget, because your "real" offer is 25% higher (€1.00 instead of €0.80)
The same positions	You can bid up to 20% less for the same results, so your cost per click drops

Two honest notes. First: the saving is "up to" 20%. The exact size depends on how crowded the auction is for your products; most accounts see between 10% and 20%. Second: with automated bidding (target ROAS, maximise conversions) Google adjusts bids itself, so the advantage shows up as more conversions for the same budget rather than a visibly lower CPC overnight. Always compare 30 days before with 30 days after, not yesterday with today.

What changes and what does not in your account

Moving to a partner CSS is an administrative change, not a technical one. Concretely:

Unchanged:

Your Google Merchant Center account: still yours, same ID, same product feed, same approvals.
Your Google Ads account: same Shopping and Performance Max campaigns, same history, budgets and bidding strategies.
Billing: you keep paying for clicks to Google Ads, as before.
Positions and performance history: campaigns do not stop and do not "relearn" from scratch.

Changed:

The label under your ads: from "By Google" to "By [your CSS]". Shoppers rarely notice; the click still lands on your site.
The amount that enters the auction: 100% of the bid instead of 80%.
The entity that "places" the ads on your behalf, visible only in Merchant Center.

A self-service CSS such as Bigconvert CSS does not manage your campaigns and has no access to your Google Ads account. It only places your existing ads through its own domain. Some agencies include the CSS in their campaign management service; then you pay the agency fee and the CSS comes with it.

Does it work with Performance Max and free listings?

Performance Max: yes. The Shopping component of Performance Max campaigns (the product ads from your feed) is also placed through a CSS, so the same auction rule applies. The Search, Display, YouTube or Discover components have nothing to do with the CSS and stay as they are.

Free listings in the Shopping tab: they do not go through an auction, so there is no cost to reduce. They stay active whatever CSS you use.

Standard Shopping campaigns: yes, fully.

What a CSS costs

CSSs charge in one of three ways, and the difference matters more than it seems:

A flat monthly fee, whatever your ad budget. Bigconvert CSS costs €18.99 per month per store, no commission, cancel anytime. On a €1,000 monthly budget, a 15% saving means €150 saved for €18.99 paid.
A percentage of ad spend (usually 1–5%). Worth it only for very small budgets; from a few hundred euros a month it costs more than a flat fee.
Included in an agency's fee for managing your campaigns. No separate charge, but you cannot take the CSS without the agency service.

Some CSSs also offer a free trial. Whatever the model, check that there is no set-up fee, fixed-term contract or cancellation penalty.

How to switch to a partner CSS, step by step

Choose the CSS and give it your Merchant Center ID (the number in the top right corner of Merchant Center). With Bigconvert CSS you fill in a form and pay the subscription online; no signed contract needed.
The CSS sends an association request from CSS Center, Google's platform for CSSs. You get a notification in Merchant Center.
You approve the request in Merchant Center with one click. From that moment your ads are placed by the new CSS. It usually takes minutes; rarely a few hours.

You do not change your feed, campaigns or bidding settings. If you ever want to go back to Google Shopping or move to another CSS, the procedure is the same in reverse, and nobody can stop you.

Is it legal and approved by Google?

Yes. The CSS programme was created and is run by Google following the European Commission decision. Google vets every CSS before approving it (a working comparison site, at least 50 distinct stores per country, a registered office in Europe), lists it in the official directory and monitors compliance. It is not a "trick" and breaks no Google Ads policy; Google itself encourages stores to compare CSSs and choose.

Google can also grant a CSS Premium status, reserved for the largest and best-certified CSSs. The status does not change the saving (the auction rule is the same for every CSS), but it says something about the partner's size and experience.

About Bigconvert CSS

Bigconvert operates its own Google-approved Comparison Shopping Services: Bigconvert.com, Bigconvert (gen.ro) and ProductXL.com. The company was formed by merging two Romanian companies with a track record in the CSS programme: Viziune Grafică, whose Tidyshopping comparison site became the first Romanian-born CSS with Google Premium status in 2019, and Glew Solutions, whose Epio CSS earned Premium status in 2023. Since the rename to Bigconvert, the current status is Google CSS Partner, with Premium re-certification expected in January 2027.

As of October 2026, more than 2,000 online stores across Romania and Europe run their Google Shopping ads through Bigconvert's CSS domains, with over 3.5 million clicks a month. The service is self-service: €18.99 per month per store, no commission, activation in 5 minutes, cancel anytime.