Yeah, but...
So long as the restaurant is small enough that the receipts are done by hand (i.e. there aren't preset names and amounts for each item in the till), and given that the vast majority of restaurants avoid you having the menu and the bill at the same time, you'd have to be very alert to notice that all of your dishes cost 50p more than they should have.
( RadioElectric, Wed 13 Jul 2011, 4:09, Reply)