A feedback thread is definitely a good thing to have, but as seen here; not a preventative. The nice thing with iTrader is that it's directly attached to the person's profile, and shows up with every post the person makes. VERY easily identifiable, and when there's a -1 or more sitting on an iTrader directly attached to the person, you dont have to research them to know its a bad deal.
iTrader is just a mod for vbulletin:
iTrader v2.0.1 - vBulletin.org Forum Because this forum is already vbulletin, you're good to go.
Just a suggestion. I know it wont help the situation at hand, but it'd be a preventative for the future.