We once spent a small amount of money advertising with Google, just to try it out for a new business. The referring page with the most "visitors" was literally

We once spent a small amount of money advertising with Google, just to try it out for a new business. The referring page with the most "visitors" was literally a bunch of buzzwords in something like 6pt grey on slightly darker grey text. It was like some sort of spoof stereotype of an ad-abusing landing page, which any crude detection algorithm I could imagine would have red-flagged. Various other pages were similarly obviously deceptive. We wrote off the small amount of money since it wasn't worth legal action to recover it, called it a lesson learned, and none of my businesses has ever given Google a penny in ad spend in the years since.