I kind of like the trust factor. Scamming should be allowed. I mean would you walk up to someone you don't know, and buy something that you aren't even sure of, and just hand them tons of money? No, I doubt you would.
I mean if you really want to do a trade with a stranger, you could tell them to drop the item on the other side of the level, you could right click it and make sure it's what you wanted, then drop your item/money, and then both of you run to the other side and pick it up. Not that hard.