the same kind of accusation was poisonning google ads for a long time but it was called click fraud. numerous customers were suing google over billing them for fake clicks. Ultimately, google proved to be better than other sources of online advertising regarding fraud detection, and so people continued to buy ads.

The problem is the same for facebook. Major advertiser track clicks up to purchases over months , sometimes years. So they are perfectly aware of which users are bogus, which impression are actually never seen, etc. Ultimately the only thing that counts is whether the investment is worth it.