A blended ROAS can hide cannibalisation. Here is a clean way to test whether Performance Max is finding new demand or harvesting the demand you already paid to create.
A campaign can look efficient while doing very little new work.
The number that creates false comfort
Performance Max reports a pleasing blended result because it can collect signals across Search, Shopping, YouTube, Discover and Maps. The problem is not that the campaign uses several surfaces. The problem is that a blended result can hide whether the campaign created a booking or simply intercepted someone who was already looking for your brand.
This matters most for operators with strong local reputation, seasonal PR or a large returning customer base. Brand demand is valuable, but it is not the same thing as incremental demand.
Four questions to ask before celebrating
First, what share of conversions are new customers? Second, what happens to total bookings when brand coverage or PMax is restricted in a controlled market? Third, are the search terms and product groups aligned with the margin you need? Fourth, can you explain where the campaign found the customer before the final click?
Do not treat the platform’s “new customer” label as perfect truth. Reconcile it with CRM, booking and repeat-visit data where possible. A household can look new to an ad account and familiar to the business.
Use an incrementality test
Choose a region, time block or campaign split that can be compared fairly. Hold other major changes steady, record total bookings and watch branded search, direct traffic and organic demand together. The point is not to create a perfect laboratory; it is to stop a single attribution window making the decision for you.
Protect useful brand coverage deliberately
If brand search is cheap and helps customers complete a booking, keep it. Give it a clear role and budget rather than hiding it inside PMax. The issue is not brand presence; it is confusing brand harvesting with prospecting.
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Separate brand search where the platform and business context allow it. Label products and services by margin, stock, season and customer type. Supply creative that states the reason to choose you, not a generic slogan. Then use placement, search-term and asset reporting as directional evidence rather than a complete explanation.
For an illustrative account, a 6.2x blended ROAS might become 3.7x after excluding existing customers and brand-heavy conversions. That is not a failure; it is a more honest number to use for acquisition planning.
The clear take
Keep Performance Max when it finds profitable new demand, not because the blended dashboard looks calm. Split the questions, test the counterfactual and let the account earn its budget by creating customers you would not have got anyway.
The discipline is especially important before a peak season. If the campaign has spent three months harvesting known demand, it may look excellent until competitors enter the auction and the existing pool runs thin. Establish the baseline while the account is healthy, then you can recognise genuine prospecting when it appears.
Keep the thinking connected: PPC & Google Shopping for sports retailers or explore the related service.