Which is often not possible because clicking an ad generally closes the ad. And there's no incentive for users to report, by design IMO.

They could have a separate ad-reporting UI in every ad-running app (so you can report stuff later), and they could reward valid reports by skipping all ads on their network for a month or something, but doing that would reduce fraud, and that means reducing their profit. So none of them do it.

I'd say they probably need an oversight committee with teeth, to strongly punish every single violation (so the networks develop functional defenses), but they'll probably just VW-emissions-fraud their way around it.