Do you relax when you see a sign at the checkout that says, "We guarantee our scanner price is correct or you get the product free"? Well, don't. While systems are getting a lot better, many errors still occur at the checkout. Don't blame the cashier or the scanner. The problem is with the prices being put into the computer system. For specials, especially on the first day of a sale, bring the newspaper ad with you and watch the register's display to make sure the scanned prices are correct.