Advertisers simply don´t know. The reason most of them don´t know is because there are virtually no tools available that can distinguish between a real user and

Advertisers simply don´t know. The reason most of them don´t know is because there are virtually no tools available that can distinguish between a real user and a fake user. Only FB can make that assessment with some degree of certainty and even that can´t be trusted. External partners have been given a choice: either advertise at the risk of it being some garbage traffic, or not advertise at all. And for obvious reasons, the latter is what people choose to do.