I sometimes deliberately search for barebackers, older women or BBWs JUST so I can blacklist them and they won't turn up on my regular search. which may be a little strange as you can set your search to exclude these. But, it's for the best in case some change their mind on barebacking later on, I'd still want them excluded.
Aside from the occasional mass purge, I just blacklist anyone with a series of bad reviews here, or who really puts me off if I come across their profile, or who no-showed on me before. The blacklist is over 1000 names long now