(Customer approaches cash desk with two t-shirts with a price tag of $14.99 each. I scan the t-shirts.)

Me: “Oh, they scan at $7.99 each.”

Customer: “The sign on the table where I found them says that they’re 2 for $20.00.”

Me: “I know, but they scan at $7.99.”

Customer: “…but the sign says 2 for $20.00.”

Me: “I know, but head office must have changed the sale and updated the computer before we had a chance to change the sign. So you can buy the shirts for $7.99 each.”

Customer: “I don’t care what price comes up in the computer. The sign says 2 for $20.00 so you have to sell them to me at that price!”

Me: “Okay.”

(I override the $7.99 price in the computer and change it to $10.00. The customer pays two dollars more per shirt than he has to and smugly goes on his way.)