In my opinion:

It is YOUR responsibility to deliver payment.
(If you sent payment and it did not arrive because of a torn envelope. Would the seller want you to re-send? Yes, a reasonable expectation)

It is HIS responsibility to deliver goods.
(If he sent good and it did not arrive because of a torn envelope. Would the buyer expect it to be re-sent? Yes, again a reasonable expectation.)

What's good for the goose is good for the gander.
UNLESS CLEARLY SPELLED OUT PRIOR to making the deal.