Obvious to a human manually looking at the account isn't obvious to a computer system that has to pick them out a huge dataset. You will never be able to ban Fiverr type accounts because for the same reason residential VPNs work well. You're paying someone who has a clean record and will send all the right signals.

HN works because it's niche. It can be moderated by a handful of people. Once you cross the "can't be moderated by humans" threshold of size you're solving a completely different problem.

I won't knock you for saying "well then you shouldn't exist at that scale" but that's a non-answer for the real world where giving up PII in exchange for participating in a huge social network is a trade enough people are willing to make that you feel pressure to do it in order to get in.