If you kick up enough fuss in many stores you will probably get your way but, in fact, the display of a price is generally regarded as an invitation to treat and there is no obligation on the store to sell at the price displayed or even to sell the item to you at all if they choose not to. By attempting to purchase an item, the customer is making an offer and only after accepting this is the store legally obliged, by the contract then entered into, to sell the item at the agreed price. It's good customer relations for many stores to sell items at the price displayed when there is an error, but if the price discrepancy was large they would probablyprefer not to. After all, it is very easy to exchange price tickets in a lot of stores...