After discussing this issue at length with PayPal, it is only necessary for the seller to provide proof of shipping by common carrier, in the form of a Delivery Confirmation tracking number for USPS, or the tracking number of another common carrier. It is the equivalent of shipping FOB Seller's Dock. Title to the property transfers at the point of shipping by common to the buyer at the moment of delivery to the common carrier.

The mistake that some sellers make is that they do not provide proof of shipment, in the form a a tracking number. All of my outgoing packages are sent with USPS Delivery Confirmation. As soon as the US Postal Service accepts the package, as evidenced by the USPS Delivery Confirmation receipt and tracking number, legal ownership of the property is transferred from the buyer to the seller, and responsibility for safe delivery becomes the responsibility of the common carrier. The legal issue then becomes, for loss or damage, a liability issue between the new owner and the common carrier.

Unfortunately for the buyer, there is little chance of any buyer getting reimbursement from USPS without insurance or registered mail. I'm not an attorney, but I did take Business Law I and II, and also had a nice long chat with PayPal Customer Service, who confirmed my belief.

In the past, each time a claim was filed against me, the only requirement PayPal wanted satisfied to provide a tracking number. When I asked them if the seller maintained liability if the package was shipped, and had a tracking number, was lost by the carrier and not delivered, I was told all I needed was the tracking number, which would show it was accepted by the post office. Then it became the buyers problem the package was not insured or shipped by registered mail.