Er.'fraid that is not correct. The price on an item is an invitation to trade. If a retailer incorrectly prices an item and realises it at the point of sale they are perfectly within their rights to withdraw it from sale. That's the situation under English law anyway(see Misleading Prices - Consumer Protection Act 1987). If a retailer incorrectly advertises an item for sale and then refuses to honour the price you are within your rights to report them to the Trading Standards people who may investigate it and take further action if they feel their was a deliberate attempt to mislead.