At CoinMap, I can find several coffee- and other brick-and-mortar shops that apparently accept bitcoin payments. How do these transactions work? Do I have to stand at the counter for 10 minutes and wait until transaction gets confirmed, do they use some kind of trick to make the transaction time bearable?
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2 Answers
Depends on their infrastructure. If they use an intermediary (like bitpay or something) it will be instantaneus, since bitpay is the one that takes the risk for double spends and accepts payment fast. In case they have their own infrastructure, it may depend on what they do, if they accept one confirmation for the payment it may not take much otherwise it may take longer. I don't think any of those shops do that by themselfs, most probably the will have an "acquirer" for bitcoins.
The effort to successfully pull off a double-spend is disproportionate to the cost of paying for a couple cups of coffee. Not only is the window smaller than 10 minutes, but when the double spend actually works, you might not be able to go back to that coffee shop. ;)
Therefore, the risk of accepting such a small transaction with zero confirmations is acceptable for a store in order to save the customer the time to wait around, and stores usually should accept your payment with zero confirmations i.e. as soon as the store's device shows the incoming transaction.
If a huge sum, say more than $1000, is involved, it would probably be acceptable to the paying party to wait for at least one confirmation.
When the store uses a payment processor, the payment processor will accept the payment at zero confirmations and carry the risk of a double-spend.