AFAIK, permaban is for plagiarism, spam boosting, and ban evasion. As for now, you can just keep reporting his posts and you can give some negative trust entries or/and support the flag.
I believe accounts can be nuked for a variety of reasons, ranging from spam to scam attempts. This applies to newbie accounts
Require at least one merit to become a Junior Member (bots will never rise past Newbie status then and can be nuked once spotted).