A prime example of this is the supermarket,quite often they make mistakes either way, quite often not giving me the specials advertised and overcharging me, and i don't have the time to be bothered checking my till receipt right away,not until i get home, so i figure they have ripped me off quite a few times, so when its in my favour i donot go back,too much time involved, i often don't bother going back either when it is not in my favour, so kinda works out in the end i think,so many people never check their supermarket till receipts so they fair pretty well out of it i reckon.