PMax Brand Cannibalisation Teardown
How an efficient-looking PMax campaign can capture branded demand and overstate incremental performance.
PMax can serve against branded queries and existing demand, then report conversions that Search or direct traffic would likely have captured.
The leak
PMax can serve against branded queries and existing demand, then report conversions that Search or direct traffic would likely have captured.
The evidence
Compare branded query exposure, brand Search volume, new-customer share and the change in total account conversions—not only PMax ROAS.
The fix
Apply brand exclusions where appropriate, separate brand reporting and judge the account on incremental non-brand outcomes.
What I would not change
I would not pause PMax based on suspicion alone. Establish a baseline, change one control and measure total-account impact over a valid window.