I try to always watch as the items are being scanned and check the receipt before I leave the store...and count my change, if any! Mistakes are made on both parts...I have, upon occasion, not paid for something (fell under/in purse, in cart, etc and neither the cashier nor I spotted it at the time (this usually happens around birthday and Christmas when I'm trying to hide the item from a family member!). I go back into the store and explain my mistake and pay for the item. I'm thinking some cashiers aren't used to that kind of honesty because I sometimes get a strange look.