I would say that the risk is less than that of the USPO "lost" my package and much less likely that the USPO insurance would pay for it.
But it does happen ... I can think of one very healthy gentleman that posted a lot on our local forums and that I traded with regularly that very abruptly went radio silent (not just with me). Could have been due to any number of things but since he was manning the local drive-through free vaccines with his co-workers, I have always assumed that that may have been the cause.
As far as ettique goes, I think the buyer and seller need to agree on terms. You're on shaky soil if you ask to revise those terms in the middle of a transaction.
JC189, glad you're feeling better and I expect that I would have found the exception equally acceptable given your perception of how it was handled.
