You like the elevator pitch. Performance Max uses everything Google has at once. Search, Display, YouTube, Gmail, Discover, Maps. Automatic remarketing baked in. The algorithm figures out where to find more customers like the ones you are already getting.
So you run your campaign.
The first few days are mixed. Some good leads, some bad. Then the poor-quality leads start flowing through. Then more. Then a flood.
What is happening: Google has zoned in on a neighbourhood that generates leads cheaply.
These come in many shapes. From what I have seen, the most common source is unscrupulous publishers who run AdSense. They get paid for every click Google sends their way, so they hoover up the cheapest traffic they can find (low-quality click farms, junk networks, traffic exchanges) and dump it onto pages running your ads. No grand reveal here. These people are not going to buy your product.
The mechanism
If you tell Google something is a conversion, it will bid higher to attract more similar traffic. That is the whole loop.
PMax amplifies it because it uses cheap traffic sources, typically involving third parties (not Google itself), where Google cannot directly control the quality.
So you need to be very careful about how you define a conversion.
Where it breaks #1: unconditional form submissions
Counting any form submission as a conversion gives the dodgy publishers above all the room they need. They use networks that fill out your forms en masse (not real customers, just people or bots submitting forms at scale). Those submissions register as conversions in Google. Google keeps bidding for that traffic. The publishers keep buying it for next to nothing. Money flows from you, through Google, to them.
Where it breaks #2: WhatsApp clicks
Most people track WhatsApp by firing a conversion when someone clicks the WhatsApp icon on the website, usually via GTM or a JavaScript snippet.
News flash: a click is not a message. It could be a competitor checking your site. It could be a bot. It could be the same dodgy networks above clicking your icon to trigger a conversion. None of those people are buying.
The fix
Be more careful about what you tell Google is a conversion.
For forms. Check the actual data in the submission before counting it. Most business owners can read a lead and instantly tell whether it is real (or at the very least, cross out complete spam). The good news: AI can now do this automatically. This is how Tagless works. Every form submission is read by AI, and only qualified leads are marked as conversions and sent back to Google.
For WhatsApp, two levels of fix:
Bare minimum: verify a real message exists. A click is not a conversion. A reply is. Google has no knowledge of anyone sending a message on WhatsApp (Google vs Meta, fundamentally). Remember the objective: identify the people who messaged AND who came in from a click on Google's ad network somewhere, so we can send that signal back to Google and tell it we want "more of these." The way you do this technically: inject a reference into the pre-filled WhatsApp message, associate that reference with the GCLID in the background, and only log the conversion when a real message actually arrives. This alone rules out competitors and bots.
Next level: read the messages. Once you have got the real message, you can analyse the conversation to gauge how much intent the lead actually has. Tyre-kicker or buyer? AI can do this in seconds. Tagless does this too.
The result: a real customer sent a message, chatted with you, and you can not only tell Google about the conversion but link it back to the specific ad click that drove the interaction. The reference in the message maps cleanly to a GCLID (Google's ad click identifier), so the conversion you send back is tied to the click that originated it.
The bottom line
All of these obstacles are solvable. They are just not solved out of the box with Google Tag Manager. And consent adds another layer of complexity on top, because the base solution is bespoke to begin with.
This is where Tagless comes in. Set it up in 2 minutes and every problem above is handled out of the box. The conversion definition becomes the thing it should be: real, human, qualified leads. PMax stops finding spam and starts finding customers.
You do not have to worry about any of the failure points. There are two kinds: the plumbing (setting things up correctly), and the parasitic actors in the system. GTM not configured correctly. Cookie consent banners breaking your conversion pipeline. Bots and click farms acting as parasites on your ad dollars. It all just works.
PMax is Google's state-of-the-art digital advertising. They have unequivocally promoted it as the future at every point. The best news: lead-based businesses have not embraced it yet, precisely because of the problems above. Tagless solves them easily and comprehensively, so you can future-proof every PMax ad you run.
For the wider picture on why PMax for leads is broken for almost everybody, and the cheap-bid opportunity that creates, see PMax for leads: everyone hates it, which is exactly why it works.