1. People spitting for lubrication (that shit was quite popular in the 2000s for some reason, ant it still happens occasionally). Gross
2. Fake threesomes/swaps passing off as real. The hub is full of this shit, people with green screens pretending to do a spitroast, or a guy who goes off camera, puts a cock sleeve/changes his underwear, etc.
3. Models who will obviously do nudes/hardcore/etc at some point, but wait until they're way past their prime to do so.
4. Models who cover themselves with tattoos afterwards. Like, if you start your career with tattoos, that's fine, but if you start your career without tattoos and then cover yourself with them. If you started your career without tattoos, stay without them. Maria Ozawa was, for me, the worst offender in this one.
5. Same as above but replace "tattoos" with "fake tits". If you start your career with them, fine, but if you start with naturals, guess what? Your fans probably want you to keep them natural.
There's probably more but those 5 are off the top of my head.