If you are spending thousands per day you should be backing out real time ROI/LTV which eliminates nearly all potential fraud.

The performance ad market moved from pay per impression to pay per click and then finally to pay per conversion years ago. Pay per conversion is the foundation of Facebook's lookalike audiences and Google's long-tail search campaign tools. When I see problematic campaigns these days it's usually because the media buyer hasn't set up their funnels/KPIs correctly.