Finnish Design Shop CSS Test
We Tested with Finnish Design Shop: Does Third-Party CSS Deliver on Its Promise of 20% Efficiency Gain in Google Shopping?
+18.3%
Incremental Sales
+16.3%
Margin ROI
-10.7%
CPC Reduction
Client
Objective
In Google Shopping advertising, third-party CSS is often marketed with a promise of up to 20% better efficiency: either more clicks and sales with the same budget or significantly lower CPC and better ROAS. We wanted to find out with Finnish Design Shop whether this promise actually shows up in business metrics. The CSS model (Comparison Shopping Service) applies only to Europe (EU/EEA, United Kingdom, and Switzerland) and its background stems from an EU competition law decision from 2017. The key sales argument of third-party CSS relates to cost structure. When Shopping advertising is purchased through Google's own CSS, Google takes approximately a 20% "margin" before the auction. When purchasing through a partner, this margin is removed, creating a theoretical efficiency advantage. However, it's essential to note that this approximately 20% advantage is fundamentally theoretical. In practice, verifying it is challenging. Hypothesis: If third-party CSS truly brings a competitive advantage in the auction, it should show up in either more clicks and incremental sales at the same cost level, or lower CPC and better profitability.
Solution
The test was built to be as clean and comparable as possible: • Two identical Standard Shopping campaigns were run in parallel • The only variable between campaigns was the CSS used: Google CSS vs Third-party CSS This made it possible to isolate the real impact of CSS without other optimization variables.
Results
Third-party CSS showed +~30% higher impression share, meaning ads participated in relatively more auctions. But there was no growth in clicks, no lower CPC, and no growth in sales or ROI. Mere relative growth in visibility did not translate into business benefit. Google CSS, on the other hand, showed: • +18.3% more incremental sales • +16.3% better margin ROI • +8.8% more clicks • –10.7% lower CPC while having –22.3% lower impression share. In other words: Google CSS clearly won in the metrics that actually matter. Conclusion: Third-party CSS did not deliver on its promise of a 20% efficiency gain in this test - quite the opposite. Although relative impression share increased, real business benefit was not achieved. In Finnish Design Shop's case, Google CSS proved to be a clearly higher-quality and more profitable option for Google Shopping advertising.