If someone sold Bitbills (
http://bitbills.com/) via PayPal and used some kind of certified mail service, would that allow them to accept PayPal payments for Bitcoins without getting scammed?
That reduces the chance of getting scammed, but it wouldn't stop all scams. Certified mail service would show it was received, but it's very difficult to prove what was actually received. Then on top of that you have to explain to investigators what Bit Bills are. Most likely they're not going to care and just rule for the buyer.