Technically a store can refuse service to anyone, within reason. If they feel that people are taking advantage of the deals unfairly then they can limit quatities. Mind you that doing so runs the risk of alienating people and losing potential sales from non sale items. It would be illegal to refuse service due to race, gender, etc.
Like I said it is their choice but in the interest of public relations it is best that they aren't too strict about all of this. Otherwise next year their customers may just go price match somewhere else.
