Why cash?

People are always more willing to trust a machine over their brain. I went into a national sandwich chain (some years ago). Ordered my usual sandwich, and the amount rung up wasn't the usual amount. Looked up at the board, it didn't indicate a price change. Pointed out to the counter person that the machine was overcharging me.

"oh yea, there was a price increase" - I pointed at the price board (unchanged). "But thats not the price". I reminded them that they have to honor the posted price, unless they wanted to be charged with fraud.

What made it particularly amusing: The manager didn't have an override so he could charge me the correct amount. (apparently they couldn't just say "misc taxable $4.73", they could only push the specific item buttons). He had a bit of a clue, and gave me the thing free.

I am sure lots of people didn't notice, and overpaid. The only reason I noticed, was that it took the total from under $5 to over $5. I happened to hand over a $5, and thus expected a few cents change, not a request for another quarter. (had they updated the sign, and not just the computer, I would have handed over the extra without comment)