Their mistake or mine, I would have gone back to pay for it. I've done it before and I always feel 1000% better when I do so. I just go over to the customer service desk and get taken care of right away.

Just think, people who do NOT come back to pay for it are really bringing the prices of items UP, since they have shoplifted in a sense. Sure you didn't KNOW you had something you didn't pay for when you left, but when you notice you didn't pay for it and don't go back, you have just shoplifted. AND are raising our prices of items!