Define a genuinely new customer
Use a documented business definition that can be applied consistently to Shopify order data. Decide how guest checkout, prior refunds, multiple emails, household overlap, and internal orders will be handled before promotion begins.
Protect the value proposition
Make the eligible products, order conditions, campaign dates, and post-purchase steps visible. The offer should attract an appropriate first purchase rather than surprise the shopper after checkout.
Measure customer quality
Track qualified acquisition cost alongside cancellations, returns, gross contribution, support burden, and later purchase behavior. Separate observed outcomes from claims of incremental impact.