What Performance Max actually is
Performance Max is one campaign buying across Search, Shopping, Display, YouTube, Discover, Gmail and Maps at once. You hand over assets, a budget and a goal, and the machine decides the rest: which network, which audience, which creative, which query.
That is genuinely powerful when you have conversion volume and clean data. It is also, by design, close to a black box. The reporting Google gives you back is a fraction of what it gives you for a standard Search campaign, and that gap is where most wasted PMax spend lives.
Where the money actually goes
The most common problem we find in PMax audits: the campaign is quietly buying your own brand traffic and billing you for conversions you would have got anyway. Brand searches are the cheapest conversions in any account, so an algorithm told to maximise conversions will hoover them up and report a beautiful ROAS.
The second is Display and Gmail inventory soaking up impressions at low intent. It looks like reach. It spends like advertising. It converts like neither.
Neither of these shows up if you only look at the top-line number. That is the point we keep making to clients: a PMax campaign reporting 8x ROAS is not evidence of anything until you know what share of it is brand.
Structure it so the reporting means something
Split by margin or by product intent, not by whatever the shopping feed happens to be organised around. If your best-margin range is buried in one asset group with everything else, the algorithm will optimise toward volume and you will never see it happen.
Give each asset group a genuinely distinct audience signal and its own creative. Asset groups are the only real lever you have inside PMax, and most accounts run one bloated group doing everything.
Keep a standard Search campaign running on your core terms. It costs you a little duplication and buys you visibility you cannot get any other way.
Exclusions are the whole game
Add a brand exclusion list so PMax stops claiming credit for people already searching for you. This single change reframes the numbers on most accounts, usually downward, which is uncomfortable and correct.
Apply account-level placement exclusions for the app inventory and made-for-advertising sites that eat Display budget. Add negative keyword lists at account level, since PMax will honour those even where campaign-level negatives are limited.
Then look at the search terms you can see. It is a partial view, but a partial view acted on beats a complete view admired.
What good looks like
Good PMax reporting separates brand from non-brand, tracks new customer acquisition rather than total conversions, and compares performance against what the account did before PMax existed. If your agency cannot produce those three things, the campaign is running them, not the other way round.
We run Performance Max on plenty of accounts. It earns its place. It just does not get to mark its own homework.