Depends. Can you show us their posts? Whether they have half a brain or not makes a big difference of how they can be treated (see ANORECTAL VIOLENCE poster who understood how to evade generic ban filters)
1) ThingNoticing: if they're an agenda schizoposter like anorectal anon or a spammer, they have telltale signs that can usually be detected with a basic regex pattern or two. Some others are harder to pick out. Make sure to avoid false positives.
2) Diversion: Imagine you are the schizo. You make your post on a fresh VPN node and it says 'go away schizo'. What do you do?
Now imagine you are the schizo. You make your post on a fresh VPN node and it says 'Your IP address is listed in rbl.efnetrbl.org.' What do you do?
Now imagine you are the schizo. You make your post on a fresh VPN node and it says 'Due to spam raids from wojak.party, you must have the correct password to make a new post. Email [email protected]
for more information.' What do you do?
3) Social manipulation, like >>7076
said. You can sometimes constructively manipulate them. Insulting builds resistance.
Of course, some are too thick and socially autistic. I know one who has a telltale habit of posting ten train-of-though posts then responding four times in a row to anyone who insults them, attempting multiple personalities without realizing how obvious their samefagging is (they don't even switch grammar styles and are ESL).