The key point
With a 20% bid margin, a £1 Google Shopping bid puts £0.80 into the auction. Removing that margin lets £0.80 buy the same auction value, or lets the full £1 compete.
Use Google Shopping CSS as the comparison
Google explains that its Shopping CSS deducts a fixed percentage margin from merchant bids. GMVLY’s bidding illustration uses a 20% margin: from a £1 bid, £0.80 enters the auction. The Google guidance linked below explains the mechanism without specifying the numerical rate.
This comparison is with Google Shopping CSS. If you already use another independent CSS, you may already receive the same auction advantage. Compare service, subscription price and terms rather than expecting another 25% gain simply from changing independent partners.
Option one is a 20% lower bid for equivalent auction value
A £1 bid through Google Shopping CSS becomes £0.80 after the illustrated margin. A £0.80 bid through GMVLY puts £0.80 into the auction. The effective auction bid is the same, while your bid is 20% lower.
The calculation is (£1.00 − £0.80) ÷ £1.00 = 20%. This is a comparison of bids, not evidence that your realised average CPC will fall by exactly 20%.
Option two is 25% more bidding power at your previous bid
Keep the previous £1 bid and the full £1 enters the auction through GMVLY, compared with £0.80 in the illustrated Google Shopping route. That is £0.20 more effective auction value relative to the old £0.80 baseline.
The calculation is (£1.00 − £0.80) ÷ £0.80 = 25%. The percentages use different denominators. They describe two ways to use the same advantage and do not add together.
Connect the advantage to your Shopping target
Decide whether your PPC team wants to pursue more volume, protect efficiency or adjust bids. Actual click costs and results still depend on auction conditions and your bidding strategy. An auction advantage is not a guaranteed increase in sales or ROAS.
Record the campaign baseline before a switch: spend, clicks, CPC, conversion rate, sales value and ROAS. Track promotions, stock changes and major campaign edits during the review period. A before-and-after result can be useful context but does not isolate the switch as the cause.
With GMVLY Self serve CSS, your team keeps managing and funding campaigns and maintaining the feed. The approved subscription is £15 per verified Merchant Center monthly or £150 annually. The initial 30-day trial starts after switch verification and payment setup.
Sources and further reading
Review the advantage against your current CSS
See the two bidding options and the Self serve CSS plan, then discuss your Merchant Center setup with us.
Explore Self serve CSS →