just my tuppence worth , how are you ever going to get trusted as people will avoid buying from people without "trusted Status" its a bit like buying of ebay from someone with no feed back, good idea in theory but the buyer needs to take care its not the forums job to look after you money,
one way you could get around this would be if a Trusted person (admin for example) held the cash and only released it when the goods were received as described, not for all sales but only the odd one where both seller and buyer agree, but this could be a lot of hassle for the middle man/woman
Rob