I think the problem is that a buyer can come back up in a matter of minutes and scam again. There's really nothing much to stop it because of TOR and bitcoins anonymity. The same can be said for vendors, but those can be scrutinized and have to at least pay money to become a vendor. Doing that takes time and money - even though a scamming vendor can easily overcome their deposit rather quickly it's still a deterrent.Not saying it's perfect, but by looking at it from that perspective I can see why they do it that way. As a vendor you can always report a suspect buyer, but even if we delete the account they could buy from you again right away.