That's one of the reasons stores offer sales, coupons, and similar: they allow stores to effectively offer different prices to different people, extracting more total revenue than if they had to charge everyone the same price. A store could never get away with directly saying "we charge more if you have more money". But they can offer coupons and sales, which have the same effect: those who take the time to clip coupons and watch for sales pay a lower price (and thus buy anyway), while those who don't pay a higher price.