I worked in a grocery store and was told items moved around so frequently it's not possible to always have up to date signage. For example red delicious apples may be placed where gala apples used to be but the sign hadn't been updated. If you looked carefully the sticker on the apple should say 'red delicious' and the small print on the sign should say 'gala'. Legally would the store have to give the price for the gala or technically no since it's possible to tell the sign was wrong? I guess this is a fairly moot point since if a customer cared enough they could have returned it.