You should at least use the trust system to contain scams. At the very least it should prevent people from being scammed by other users.
And you can't really have merit = reputation. High-quality posts don't always correlate with a user being trustworthy. Perhaps a large portion of the time, yes. But then how would you tailor to successful transactions between individuals? It doesn't seem right to send them merit as that was the argument with trust: bad post quality ≠ scams.
Why can't it exactly go hand-in-hand?