How many people/businesses check twenty dollar bills, or five dollar bills for counterfeit before allowing the customer to take their sandwich/beer?
I guess it depends where you are - in China every 50 or 100 RMB note (rough equivalent to 10 and 20 dollar bills) is generally checked (if not by a device then by close visual inspection) as there are so many fakes going around.
When selling items of low value 1 confirmation should be fine (you only really need to wait multiple confirmations for very large amounts).
Yeah, it will be a sad day when the first double spend happens, which to my knowledge hasn't occured yet in the brick & mortar space.
