What a CSS is, and why it can lower your Shopping CPCs
Comparison Shopping Services can place your Shopping ads on Google in Europe. How the programme works, where the price advantage comes from and how to choose a partner.
- A CSS is a comparison service that can run Shopping ads for merchants in Europe.
- Ads placed through a CSS other than Google’s own let the full bid enter the auction, an advantage commonly cited at up to 20%.
- Your feed, campaigns and Merchant Center stay the same. Only the CSS behind them changes.
What a CSS is
In June 2017 the European Commission fined Google 2,42 billion € for giving its own comparison shopping service an illegal advantage in search results. To comply, Google opened Shopping ads in the European Economic Area to third-party comparison services. They are called Comparison Shopping Services, or CSSs, and they can place product ads in Google’s Shopping results on behalf of the merchants they work with.
- DEFINITION Comparison Shopping Service (CSS)
- A comparison site that lists products from many stores and is approved by Google to place those products in Shopping results. Every Shopping ad in the countries covered by the CSS programme is served through one CSS, shown under the ad as “By [CSS name]”.
Google’s own comparison service, Google Shopping, is one CSS among many. It was separated into a standalone unit that has to cover its own costs. If you have never chosen a partner, your ads run through it by default.
The programme covers 21 European countries: 19 in the European Economic Area, plus the UK and Switzerland. It applies wherever your ads are shown, not where your company is based.
Where the lower CPC comes from
When your ads run through Google Shopping, part of every click pays for Google’s comparison service as a separate business. Independent CSSs don’t carry that margin, so the same bid buys more auction strength. Google has never published an exact figure, but the advantage is consistently cited at up to 20%.
As an illustration, if Google Shopping’s margin were 20%, a bid of 0,80€ through an independent CSS would compete like a bid of 1,00€ through Google Shopping. Seen from the other side, a merchant still on Google’s CSS would have to bid 25% more to reach the same position.
| Through Google Shopping | Through an independent CSS | |
|---|---|---|
| Auction | Same auction | Same auction |
| Margin on each click | Google Shopping’s margin | No Google Shopping margin |
| Effective CPC | Standard | Lower for the same position |
| Feed and campaigns | Merchant Center | Merchant Center, unchanged |
How to use the advantage
The discount doesn’t appear as a refund or a line in Google Ads. It shows up as better results for the same settings. You can spend it in two ways.
| Keep the same bids | Lower your bids | |
|---|---|---|
| What happens | Your ads win more auctions | You pay less per click |
| Effect on traffic | More impressions and clicks | Similar traffic |
| Effect on cost | Similar CPC, more volume | Lower total spend |
| Best when | You want growth | You want margin |
Automated strategies such as target ROAS, target CPA or Performance Max benefit too. They need a few weeks to learn the new auction conditions, so judge the results after a full learning period rather than the first days.
What changes for you
Very little day to day. You keep your Merchant Center account, your feed and your Google Ads campaigns. The CSS is linked to your Merchant Center, and from then on your ads carry its name instead of “By Google”. Campaign history, quality and performance data stay where they are.
- Pick a CSS partner. Check the markets it covers and the service model it offers.
- Link your Merchant Center. Your partner sends the request and you approve it in Merchant Center.
- Check the label. Once the link is active, your ads show the new CSS name.
- Keep optimising. Bids, budgets and feed quality still decide your results.
How to choose a partner
Most CSSs offer the same auction advantage. The difference is in what comes with it.
- Markets. Make sure the partner covers every country you advertise in.
- Service model. Some only provide the CSS label. Others run the campaigns for you.
- How you pay. Monthly fee, a share of spend, or a CPA only per validated sale.
- Comparison site. A CSS must run a real comparison site. A good one can send you extra traffic of its own.
A short history of the programme
The 2017 decision found that Google had favoured its own comparison shopping service in 13 EEA countries, placing it at the top of results while demoting rivals through its search algorithms. The Commission reported sudden traffic drops for some rival comparison sites of 85% in the UK, 92% in Germany and 80% in France.
Google’s remedy was to let independent comparison services compete for the same Shopping ad space on equal terms. Google Shopping became a separate unit that pays for its place in the auction like any other CSS, which is why its margin is built into every click it serves.
Common misconceptions
| Myth | Reality |
|---|---|
| A CSS gives you a refund on clicks | No refund appears anywhere. The advantage is in how much of your bid enters the auction. |
| You need a new Google Ads account | No. Your account, campaigns and history stay the same. |
| It only works with manual bidding | Automated strategies benefit too, after a short learning period. |
| Every CSS is the same | The auction advantage is similar, but markets, service and pricing differ widely. |
How to measure the switch
Because nothing else changes, the switch is easy to read if you keep everything else stable for a few weeks.
- Note your baseline. Record impressions, clicks, CPC, conversions and ROAS per market for the four weeks before.
- Keep settings stable. Avoid big changes to bids, budgets or the feed during the first weeks.
- Compare like with like. Use the same weeks of the previous year if seasonality is strong.
- Read impression share. A rising impression share at similar spend is the clearest sign the advantage is working.
What the advantage means for a budget
Because the advantage applies to every click, its value grows with your spend. A simple way to picture it is the budget needed to keep the same positions.
| Illustrative monthly spend | Through Google Shopping | Same positions through an independent CSS |
|---|---|---|
| Small shop | 2.000€ | Around 1.600€ |
| Medium shop | 10.000€ | Around 8.000€ |
| Large shop | 50.000€ | Around 40.000€ |
The table assumes a 20% advantage. Real results depend on your categories and competitors, and many merchants choose to reinvest the difference in more traffic instead.
Who benefits most
- Merchants still on Google Shopping, the default CSS, who have never chosen a partner.
- Categories with high CPCs and tight margins, such as electronics.
- Merchants advertising in several European markets at once.
- Teams that want the advantage without changing how they work.
Same feed, same campaigns, same auction. A CSS just lets more of your bid count.
Quick answers
Is a CSS the same as an agency?
No. A CSS is a comparison service approved by Google. Some CSSs also manage campaigns, but the two roles are separate.
Can I use more than one CSS?
Yes. Google lets you work with several CSSs at the same time, although each offer in an auction is served through one of them.
Does it work outside Europe?
The CSS programme covers 21 European countries: 19 in the EEA, plus the UK and Switzerland. It doesn’t apply elsewhere.
Will I lose my campaign history?
No. Your campaigns, settings and data stay in your own accounts.
Does it affect free listings?
CSSs can also show products in free listings, but the CPC advantage only applies to paid Shopping ads.
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Sources: European Commission (press release IP/17/1784), Google Merchant Center Help.
