Definitely not standard practice. There will always be bad actors, fraud, spam, etc, when so much money is involved. But most buy side systems are advanced enough to recognize bad actors and not spend money on them. So for any site/app that wants longevity in their revenue they will not implement shady tactics and they’ll earn high cpms.

Brands with real budget employ teams of people to avoid serving on the inventory you’re discussing. Nike blocks like 99% of available inventory.