Curious about this. If you go to the post office and get cash is that reversible somehow?
I don't think there is any way to make a fiat payment any more irreversable than a cash transaction.
I mean cashing a money order at the post office (as opposed to depositing it through a bank, as was mentioned earlier on the thread). I think they ask for ID so theoretically they could come after you to get the cash back if it turned out the money order was no good. Is that possible? I have no idea.