Ok let me state first that coffee is an important nutrient.
Second, if I was a barrista/cashier, and the double spend alert came up in 5 seconds, I could hold back that coffee cup.
Could you hold back that cup of coffee for 1,148 seconds?
That double spend was actually broadcast BEFORE. Because of the low fee, most nodes and miners did not see it. Until some miner that accepted low fee tx, minted it.
But some miner got his low fee transaction, because of the inconsistent relay policies among nodes. That miner rejected the second transaction, found the block, and mined the first tx.
In this case, the user sent low fee transaction first, found out it does not propagate well, almost all his peers reject it. He then sent same coins again, with higher fee.
Yes. It only appears it came after, because no one saw it, until it was in a block (the time of that transaction is the same as of the block it was minted into).
That's why it is of utmost importance that most of the network agrees on what the minimum relay fees are. Otherwise, double spends like above are possible.
..., then it should wait longer, even 1000 seconds. If that is not possible, he/she can ask for another method of payment. Also, don't forget, all offline shops have several cams.
Maybe. Now there should be software that can discern the chances of double spend. The lower the fee, the higher the chances of ds? If barista gets a signal that ds is likely, ...