What is Google CSS (Comparison Shopping Service) and How It Works

Comparison Shopping Services (CSS) are authorized platforms that submit product listings to Google and run Google Shopping Ads on a merchant’s behalf. In the European Economic Area (EEA) and UK, Google requires that Shopping ad campaigns be placed through a CSS partner. In practice, a merchant provides its product feed data to a CSS, which then bids in Google’s Shopping ads auction for that merchant. For example, Google’s own shopping unit acts as a CSS (“By Google”), but merchants may also choose any third-party CSS partner. Google’s documentation explains that “CSSs use a separate Merchant Center account for each merchant” and can bid to place Shopping ads on Google’s search results page. When Shopping ads appear, they show a “By [CSS Name]” label, indicating which comparison service placed the ad. Merchants can work with multiple CSS partners at once (alongside Google Shopping) without paying Google any extra fees – all click charges go to the CSS, not directly to Google.

Google’s own Shopping Ads platform in Europe operates as a CSS (“Google Shopping Europe”), but other firms (Acsser, Kelkoo, Channable, etc.) have become Google CSS Partners to compete. In short, a Google CSS Partner is simply a comparison shopping platform approved by Google to run Shopping campaigns for retailers. These partners handle the technical feed integration and bidding, while merchants retain control of their Merchant Center and campaign settings. As Google notes, only CSS accounts can place Shopping ads, so merchants must sign up with Google’s CSS or an alternative CSS to advertise on Shopping.

Historical Background: EU Antitrust and Google Shopping

The Google CSS program was created in response to a landmark EU antitrust ruling. In 2017, the European Commission fined Google €2.42 billion (read more at ec.europa.eu), finding that Google had abused its dominance by giving an illegal advantage to its own Google Shopping service. Before that ruling, Google had been the only CSS available in Europe and even took a 20% margin on all Shopping ad clicks. As one PPC expert explains, “if you paid €1.00 for a click, €0.80 would go into the auction and €0.20 would go to Google…as an additional margin”. This arrangement made Google Shopping inherently more expensive for advertisers.

Under the EU decision, Google was forced to open up its Shopping auctions to competitors. Google had to spin off Google Shopping Europe (GSE) as a separate unit and “operate in a demonstrably profitable manner,” meaning it could no longer subsidize Shopping ads from its search profits. In practical terms, Google Shopping Europe now adds roughly a 20% fee to merchant bids to stay viable. By contrast, competing CSS providers are not required to add that fee. This means merchants advertising via a third-party CSS can bid in the auction with up to 20% more budget than if they advertised directly through Google’s CSS. In other words, using an external CSS partner effectively lowers the cost-per-click (CPC) for Shopping ads.

The compliance changes also made Shopping ads more transparent. Ads now display the CSS source (“By Google” or “By [Partner Name]”) so users see who is running the listing. For advertisers, the key takeaway is that since 2017 any retailer in the EU can choose a non-Google CSS to compete on Shopping ads – a choice that can lead to significant savings and other benefits (see below).

Why Switch to a Google CSS Partner?

Many e-commerce businesses find compelling reasons to move their Shopping campaigns from Google’s CSS to an alternative Google CSS Partner. The main benefits are lower costs, better support and performance, and flexibility. Key advantages include:

Cost Savings (Up to 20% Bid Advantage).
Because Google Shopping Europe must impose a margin on bids while competitors generally do not, merchants can save roughly 20% on their Shopping clicks by using a CSS partner. In practical terms, a CSS partner can enter the auction with more bidding power or the same bid can win for less cost. For example, one case study notes that after switching to a CSS partner their average CPC “dropped by 33%” and total campaign costs fell 52%. As a PPC newsletter summarizes: “Most new CSS partners…don’t take a 20% margin on top of clicks. Therefore, you get a 20% discount on Shopping clicks”.
Better Service & Support.
Many CSS partners offer dedicated account management, technical assistance and feed-optimization tools. Unlike Google’s automated service, a CSS partner can work closely with you to resolve issues and improve campaigns. For example, a digital agency praised Channable’s CSS service: “any issues or challenges…were addressed quickly and effectively by their dedicated support team…[and] managing our Google Shopping campaigns and product feeds through a single, integrated platform has streamlined our operations”. In short, switching to a CSS partner often means getting personalized support, faster troubleshooting, and expert advice on Shopping campaign strategy.
Improved Performance and Reach.
Working with a CSS partner can boost your Shopping ads performance. First, lower CPCs let you bid higher or maintain budget for more clicks, improving ROI. Second, advertisers can partner with multiple CSSs (including Google’s) simultaneously. Using two CSSs means your products can appear twice in the same Shopping results page (sometimes side-by-side) without raising your own CPC, since Google ignores duplicate bids from the same merchant. This “double presence” can increase impressions and sales opportunities. In practice, retailers see higher impression share and conversion volume when they add a CSS partner. For example, an experiment with ProductHero’s CSS showed an instant 19% drop in CPC and a 4% rise in impression share.
Full Control & Compatibility.
Switching to a CSS partner is seamless. You keep your existing Google Merchant Center and Shopping campaigns intact; the partner simply starts uploading your feed under their CSS account. There is no need to rebuild campaigns or change your shopping strategy. Moreover, you gain “transparent and direct access to Google’s advertising platforms”, giving you full budget control and bidding flexibility. In essence, a CSS partner acts as a pass-through to Google Shopping Ads, often with extra tools and consultancy layered on.
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Case Studies: CSS Partner Success Stories

Real-world examples show the concrete impact of switching to a Google CSS Partner. A few notable case studies:

Swedish Retailer (Sports Equipment): An agency case study reports a Swedish e-commerce client cut CPC by 10% and boosted return-on-ad-spend (ROAS) by 10% after moving shopping ads to a CSS partner. The report states: “Lower Costs: Achieved 10% reduction in CPC…Improved Performance: Increased conversions by 5% and improved ROAS by 10%”. This was done during the peak season using ProductHero’s CSS, illustrating that even during high competition, CSS savings materialized. See the study at blog.producthero.com.
Norwegian Retailer (Toys & Hobbies): Fullstakk Marketing documented a Nordic client whose Google Shopping campaign saw dramatic gains. Within one week of switching from Google’s CSS to DataFeedWatch’s CSS, average CPC fell 33% and total ad cost dropped 52%. This freed budget to bid more effectively. As a result, the retailer’s ROAS jumped 61% while cost-per-transaction declined 48%. Analysts estimated that had they started with the cheaper CPC, they’d have saved roughly $2,000 over that period. These numbers highlight how CSS partners can quickly pay for themselves in savings and profit. See the study at datafeedwatch.com.
Sneaker Retailer (Noirfonce): Channable’s case study of retailer Noirfonce (57,000+ products, 5 countries) shows similar benefits. By integrating Channable’s CSS and feed management, the retailer’s agency increased ROAS by 30% and cut costs by 25%. Importantly, this was achieved “without raising bid costs”. In other words, better campaign efficiency rather than bigger bids drove the gains. The agency also noted that product visibility and impressions increased after the switch. See the study at channable.com.

These examples confirm that many merchants improve their Shopping ads efficiency after partnering with a CSS. In each case, avoiding Google’s extra bid margin and leveraging the partner’s tools led to lower CPCs, higher ROAS, or both.

Consider a Google CSS Partner for Your Shopping Ads

Given the evidence, e-commerce businesses running Google Shopping Ads in Europe should seriously consider a Google CSS Partner. The historical reason – EU rules forcing competition – means that every eligible merchant can benefit from the CSS program. By moving to an alternative CSS (such as Acsser or other Premium CSS Partners), advertisers can reduce ad costs, gain expert support, and potentially boost campaign performance.

In summary: Google CSS (Comparison Shopping Services) allow merchants to place Shopping ads via third-party platforms. The EU antitrust decision of 2017 enabled this open market. Today, using a non-Google CSS partner often yields up to a 20% bidding advantage and comes with dedicated service and extra visibility. As one guide concludes, choosing a CSS partner is now a must to “remain competitive as an online retailer” on Google Shopping. E-commerce marketers should evaluate Google CSS Partners like Acsser to make the most of these opportunities.

Frequently Asked Questions about Google CSS Partners

What is a Google CSS Partner?

A Google CSS Partner is an approved Comparison Shopping Service that can list your products and bid in Google Shopping Ads on your behalf in the EU, EEA and UK. Using a partner is an alternative to placing ads directly through Google’s own CSS (Google Shopping Europe).

How much money can I save by switching from Google’s CSS to a third-party CSS Partner?

Because Google Shopping Europe must add an estimated 20 % margin to stay profitable, retailers who move to a third-party CSS typically see up to a 20 % effective CPC reduction or can reinvest that 20 % as higher bids for more visibility.

Is it difficult to switch to a different CSS Partner?

No. Your product feed and Google Merchant Center stay intact. The new CSS simply submits your existing feed from its own Merchant Center sub-account. Most merchants can complete the switch in under an hour with no downtime.

Can I work with more than one CSS Partner at the same time?

Yes. Google allows the same merchant to run Shopping ads through multiple CSS accounts simultaneously. This can increase impression share and lets you test which partner delivers the best performance.

Are there any risks or downsides to using a third-party CSS Partner?

The main consideration is partner quality—choose a reputable CSS with transparent pricing, fast support and clear feed policies. Otherwise, there is no penalty from Google for using an alternative CSS, and you can revert to Google Shopping Europe at any time.