Comparison Shopping Service (CSS)
A Comparison Shopping Service (CSS) is a partner program through which retailers in Europe submit their feeds to appear in Google Shopping, often at a lower effective cost than going through Google's own CSS.
After a European antitrust ruling, Google opened Shopping placements to third-party comparison shopping services. In the European Economic Area, your products reach Google Shopping through a CSS, which can be Google's own service or one of many independent CSS partners.
It matters because the choice of CSS affects your costs. Independent CSS partners often pass along a portion of the bid advantage, which can lower your effective cost-per-click for the same placements. For European retailers spending meaningfully on Shopping, the CSS decision is a real budget lever.
From a feed perspective, the mechanics barely change. You still produce the same Google Shopping feed with the same required attributes; the CSS is the channel partner that submits those products to Google on your behalf. The feed quality requirements are identical either way.
MartechFlow produces a standards-compliant Google Shopping feed regardless of which CSS you route it through, so you can switch or compare CSS partners without rebuilding your feed from scratch.