How to Suppress Existing Customers in Google Shopping

The Repeat Buyer Problem

In most accounts we audit, 30-50% of Shopping conversions come from existing customers. These conversions inflate your ROAS, deflate your true acquisition cost, and give you a false sense of efficiency. It's the same dynamic explored in the new vs repeat spend split.

When you try to scale, you can't scale repeat buyers. You can only buy more new ones. So performance drops - not because your ads got worse, but because you were never measuring acquisition accurately.

Customer Match Exclusions

Upload your complete customer email list to Google Ads as a customer match audience. Update it at least monthly - weekly is better. Use this list to:

• • Exclude from prospecting campaigns: Ensure acquisition campaigns only target genuinely new customers
• • Create dedicated retention campaigns: Serve existing customers with different creative, different landing pages, and different ROAS targets
• • Measure the true split: Compare performance with and without existing customers to understand your real acquisition cost

PMax New Customer Goals

Performance Max has a built-in new customer acquisition goal. When enabled, you can either bid higher for new customers (value-based mode) or bid exclusively for new customers (new customer only mode).

• • Value-based mode: Adds a bonus value (e.g., +£50) to conversions from new customers, making Smart Bidding willing to pay more for them
• • New customer only mode: Only counts new customer conversions - existing customer conversions don't count toward your target
• • Customer list upload: Essential - without your customer list, Google relies on its own (often inaccurate) detection

Be aware that PMax's definition of "new customer" is limited. It uses your uploaded list plus its own signals. Any customer who hasn't purchased in Google's lookback window may be classified as "new" even if they've bought from you dozens of times.

Standard Shopping Exclusions

Standard Shopping campaigns offer more granular control. You can apply audience exclusions directly and build separate campaigns for prospecting vs retention with entirely different bid strategies.

This is one of the reasons we advocate for maintaining Standard Shopping alongside PMax - it gives you the visibility and control that PMax deliberately removes. See also the cost of brand cannibalisation.

Measuring the Split

Once you've separated new from returning, measure each independently:

• • New customer CPA: The true cost of acquiring a customer who has never purchased before
• • New customer ROAS: First-order ROAS excluding returning customers
• • Blended vs separated: Compare your blended ROAS to separated figures - the gap reveals how much retention is subsidising acquisition

When Not to Exclude

Full exclusion isn't always the right move. If existing customers have a short repurchase cycle (consumables, supplements, food), you want Shopping ads to trigger their reorders. The goal is to measure and bid separately - not to eliminate repeat customers entirely.

For brands with strong repeat purchase economics, the correct approach is dual campaigns: one optimised for acquisition at a higher CPA tolerance, one for retention at a lower cost with higher frequency.

Next Steps