What if a dishonest user sends a TX with low Fee (1 Sat/vB) to a vending machine, the machine releases the product, and after some time that user performs a FullRBF changing the destination address to one of his own addresses?
If we're talking about soda can vending machines, the guy paid 2,974 sat / $0.77 plus he's ending with another output in in his wallet for which he is going to pay extra so if we take the value of a can of soda which is 80 cents here the last time I checked, you're wasting money !!!!
If you aim for anything higher than vending machines you're simply going to get yourself in trouble, maybe in poorer countries it works but in others, there is surveillance everywhere, do you really want to get in trouble for a few $? The correct answer is: No! And nobody is going to send you merchandise worth thousands of dollars with no confirmation.
Now the vending machine owner has two options;
- either make the user wait for 1 confirmation (nobody's going to wait 10 minutes for a coca cola, I know), or:
- adapt with second layers, like lightning.
Even before that, how many vending machines that accept direct payment in BTC (no third party cards or codes or LN) are there?
Cause I have a feeling we're talking about
an anti-tiger rock solution here!