Danmarks-Posen left Google's CSS. Their Shopping clicks got 18% cheaper.
The ads built from the product feed, where the CSS applies. 30 days after the switch compared with 30 days before.
All ad formats in the Performance Max campaign together.
From 23.8% to 28.8%, for the whole campaign. Google does not split impression share by ad format.
With 4% lower spend. Performance Max moved part of the budget from the Shopping ads to other formats.
Danmarks-Posen is a Danish webshop that sells bin bags and bins. In March 2026 they moved their Google Shopping ads from Google's own CSS to The CSS Partner. Same products, same ads, same campaign. Here are the numbers from their own Google Ads account, comparing the 30 days before the switch with the 30 days after.
The result after 30 days
Across the campaign, Danmarks-Posen got into more auctions and paid less for each click, while total spend went slightly down. Impression share lost to rank fell from 72.5% to 65.6%: with the margin gone, their bids reached further.
Impression share is the share of the auctions their products could appear in where they actually appeared. Without the margin, the full bid enters each auction, so the same money can win more of them. Here, impression share rose while spend fell: the money went further, not up.
How to read the numbers
This is one account over 30 days, not a controlled test. A CSS switch moves the whole Merchant Center account at once, so there is no unchanged half to compare with. Impression share also moves for reasons that have nothing to do with the CSS. Treat it as an example of what the margin is worth on a real account, not as a promise of the same figures.
Source: Danmarks-Posen's Google Ads account, their Performance Max campaign. The Shopping figure covers the ads from the product feed in the same campaign. Periods: the 30 days before (15 February to 16 March 2026) compared with the 30 days after (20 March to 18 April 2026). Retrieved 28 October 2026.
The full method, and why we are careful with it, is on our measurement page.
What changed on 16 March
On 16 March 2026 Danmarks-Posen's Merchant Center account was moved to our CSS. Google takes a few days to move an account, and the change took effect between 17 and 19 March. Those three days are left out of the comparison.
Before the switch, Google's own CSS took a margin of up to 20% from every Shopping bid before the bid entered the auction. Through The CSS Partner the full bid goes into the auction. The ad and the price the shopper sees stay the same.
What the switch did not change
The CSS is a setting on the Merchant Center account, not in Google Ads. Danmarks-Posen's campaigns, product feed and bids kept running as before, with no pause and no new learning phase. Shoppers saw the same ads, the same products and the same prices.
The only visible difference is the small grey line under each Shopping ad, which now names our CSS instead of Google. That line is also the easiest way to check which CSS a shop uses: search for one of its products on Google Shopping and read the line under the ad.
What would it mean for your shop?
Your result depends on how much you spend on Shopping and how competitive your auctions are. The mechanism is the same for every shop: your full bid counts, and that means up to 20% cheaper clicks.