Tl;DR: If you're a coder, running a marketing experiment is harder and more expensive than coding. Wish I'd just used Facebook Ads instead...
I was always told that Google's real customers were advertisers and that they would be treated well. Guess that's not the case. Google seems to be insistent on making it as hard as possible for people to utilize their products.
The easiest shortcut to expand one's mind is to see how everyone could commit fraud. So for advertisement, the click could be fraudulent, the website owner could be fraudulent, the ad buyer could be malicious, and the ad network could be misrepresenting reality to any/all comers. It gets even better when you consider the intermediaries between most merchant and placing ads, as they tend to talk to different ad people to help make the ads, place the ads, and have an ad strategy: None of those extra steps are clean of fraud or incompetence.
Now design a working system that is remotely resistant to the different sources of fraud that every party could be committing, all with minimal human-to-human contact, as many of the steps involve interactions where at least one side is completely uninterested in talking to a human on the other side, as that would cut profits.
The end result is probably not going to be all that much cleaner than the current situation, which is optimized for nobody. It's just a little less unoptimized for Google and Facebook, because they are a bigger player than anyone else mentioned.Still they also have to start from the perspective that every interaction they might have with a smaller player could involve fraud.