Do you think that a ban will solve the situation with these accounts? I think it is not difficult to guess that if someone is so stubborn, they will find a way to return to the forum with a new name but with old habits. Therefore, in this case, and all similar situations, there is no point in a ban. All accounts have negative tags, which are great at scaring everyone away from having any connection with them. A new account bought or created, but in the same hands, is much more dangerous than an old and well-known scammer.
I partially disagree with you. I've seen scammer (who have high rank and have some negative tags) add scam website on his signature and write non-spam post on board that doesn't show trust number. If those scammer are banned and forced to make new account, at least they can't use big-sized signature or attach image without additional effort (such as obtaining merit or spending money on copper member).
Of course banning them will cause more harm to them because when they think of the rank they lose in the short range and starting over would be a big task for them, and of a true they wouldn't be free to attach images due to some newbie restrictions, and like I know no newbie would want to spend a penny of theirs to get a copper member knowing too well that they are looking for money from victims over here. Again, No one would want to give such newbie merits knowing that they don't have good intention on forum rather writing in the purpose of scamming people here.