What is preventing him from using his many forum accounts to sabotage the trust level on another person's account?
I mean the way he did it in that image was obvious and stupid, but what is there to prevent a more systematic deliberate attempt spread out over a duration of time?
His untrusted feedback (and any untrusted feedback that he may leave from alt accounts) is pretty meaningless in the great scheme of things.
There's no way to prevent, in advance, anyone doing anything if they are determined, systematic and deliberate about it.
Using Trust Ratings improperly is a problem sometimes. The Reputation Child Board is one of the checks and balance mechanism the forum has for that, but moderators are not empowered to act (unless in extreme cases) as Theymos seems to see trust as a P2P situation.