Surprised there is any doubt on this -- the buyer pays, does not get what he pays for, the carrier specifies it is lost -- seller then reimburses buyer immediately -- ONLY THE SELLER CAN COLLECT on the loss. If the carrier then recants and denies that it was lost after saying it was, delivers to the original buyer and refuses to pay the claim, the carrier should be taken to court for incorrectly stating something that led to a loss.
I was the buyer in such a transaction and could not believe that the guy would just keep my money, refuse to sign over the parcel loss collection rights, then be able to DOUBLE collect from UPS. I initiated a PayPal claim, but before they intervened, UPS paid up and he paid me -- months after the transaction. Then he threatened a negative rating if I gave him one.
I wimped out with a neutral and explanation -- he reciprocated same. Bad bad business -- shame on that kind of weasel.