This is one of the reasons that I built bidkat.com. With BidKat, scammers have to go through the trouble of making a valid offer (which can't be done with a screen scraper), verifying their offer, and then hoping that the seller contacts them before they can even start these conversations.
If the seller does happen to contact them, the conversation ends quickly once they aren't interested in paying since most sellers will have multiple offers to fall back on. While it doesn't solve the problem, we find that it raises the bar sufficiently to the point it currently isn't worth it for the scammers to bother.
If the seller does happen to contact them, the conversation ends quickly once they aren't interested in paying since most sellers will have multiple offers to fall back on. While it doesn't solve the problem, we find that it raises the bar sufficiently to the point it currently isn't worth it for the scammers to bother.