Personally I think this is a bad idea. Even if you have them blocked, maybe they still need that item you have and could offer something over the value in fg for it and you could go for it.
Its a free and open forum. Just because someone posts in your threads and you don't like them, doesn't mean they should be blocked from posting in those topics.
Furthermore, if you have a problem with someone, attempt to work it out and resolve to reach a solution. That's my best advice.
Voted No.