If you read any article about Google CSS (Comparison Shopping Service) partners, within the first minute you’ll be hit with the cliché: “Save (up to) 20% on Cost per Click.”

Yes, it is a fact; Google does indeed take this margin from non-CSS campaigns, and by eliminating it, your full bid enters the auction. But if you actually manage an e-shop with thousands of products and fully automated campaigns, this information simply isn’t enough.

Experienced e-commerce managers are troubled by much deeper questions concerning algorithms, the behavior of Performance Max (PMax) campaigns, and the loss of valuable historical data.

Let’s take a look at the two biggest myths ruling the Google Ads world and show how they work in reality.

“If I deploy multiple CSS partners at once, I will drive up my own CPC.”

This is by far the most common fear. An e-shop wants to test multiple CSSs (for example, Google Shopping CSS alongside an external partner) but is afraid of so-called cannibalization.

The idea sounds logical:

If I send the same product into an auction through two different partners, they will start outbidding each other, and I will pay Google more.

What is the reality? The exact OPPOSITE!

The architecture of the Google auction is built so that you can never compete against yourself and artificially inflate your CPC. Before entering the auction, the system recognizes that it is the same merchant (same target domain and products).

For example:
If CSS “A” bids 0.20 € per click and CSS “B” bids 0.30 €, Google will only send the stronger bid (0.30 €) into the auction. If another real competitor (a different e-shop) in the auction bids only 0.20 €, you will only pay what is necessary to beat them. You are not increasing the price against yourself.

*More detailed info in the article: Can Multiple CSS Partners Increase Your Price?

Source: Can Multiple CSS Partners Increase Your Price?

Why would you even use multiple CSSs? International experts commonly work with multiple CSSs for diversification and A/B testing of feeds. While one CSS maintains stable performance, the other can be used for more aggressive testing of XML data optimization without jeopardizing the main account.

“By changing my CSS partner, I will wipe out historical data and ruin my P.Max campaigns.”

Performance Max (PMax) works like a massive black box that needs months of learning to perform well. E-commerce managers have a panicked fear that if they switch to a new CSS partner, this box will reset to zero, and the campaigns will drop into a so-called learning phase, tanking their ROAS for weeks.

What is the reality?

It depends on HOW you execute the transition.

If you have a completely new Merchant Center account created for the new CSS, your data will indeed drop to zero. However, if a standard technical switch is performed – meaning your existing Google Merchant Center is simply linked to the Multi-Client Account (MCA) of the new CSS partner – there is absolutely no downtime. Historical data, PMax learnings, product IDs, and quality scores remain completely untouched in your original account.

Conclusion

Migrating to a CSS is no longer just about blindly saving budget; it is an absolutely essential strategic tool.

While your competition hesitates out of fear of losing data or self-cannibalization, you—armed with a technical understanding of how the algorithm and Merchant Center data sharing work – gain a massive opportunity to dominate Google Shopping without unnecessary risk.