I just talked to Paypal, and here's what I learned:
1) To qualify for Seller's protection, you must have records of shipping and proof of delivery - and keep them for YEARS. Local pick-ups and in-person deliveries do not qualify (this is stated in the Help section of their site as well).
2) As others have mentioned on a'gon, if a stolen credit card is used to pay for the goods, the credit to the seller's account can be reversed, and the seller has no other recourse but to find the buyer and try to collect through the legal system.
#2 pretty much leaves the door wide open and basically there is absolutely no security. I contacted Paypal because I knew I was about to be scammed - am selling some wheels and the buyer offered more than the asking price, was a Malaysian (he claimed) on assignment to the UK, and would send a moving company to pick the goods up... How obvious is that scam... And this is the second time on the same item... another buyer claimed they could not talk to me on the phone because they are speech impaired.
Wire transfers appear to be a lot more secure for a seller, as it shifts all risk to the buyer. But I am not sure I would want anyone out there to be in possession of such personal information either, for identity-theft purposes.