Private middleman?
I've already mentioned to dave or arun (can't remember) that a good strategy would be to allow private middleman services, therefore everybody can use his own strategy to keep a transaction safe. PMMs would have to pay a constant tax to MPGH in order to keep their services up (thus assuring a certain level of protection to both the buyer and seller), on the other hand PMMs get a small percentage for each transaction that they supervise.
This I guess will lower the scam rate, and let's be honest IM is shit, and NPCvend seems fairly shit too, they're good concepts but not ready yet to be used in everyday tradings. Then again this is merely a suggestion, I appreciate that MPGH is trying its best to make the marketplace a safer experience for all of us.