In theory, it's a decent idea but it's just too hard to implement that. Pretty much every trade takes place over MSN and we can't moderate what goes on in those conversations.
Since what Verts said is true...instead, we can switch up the rule a bit and say that if they are scammed by going first to a newcomer, they may not report the incident?
The downside with my idea is that the person who scammed will get away, =/.

