I'm going to edit the The store is not your friend post to include this section but I wanted to post it her so those who have already read the other post wouldn't miss it.
Another trick stores use is a limited time sale. Sometimes they use the wording "2 days only" or "3 days only" Sometimes it's "Hurry in! Sale prices are good only for a limited time!" or "Limited quantities!"
The point with these types of sale is to encourage you to make an impulse buy without taking the time to think it through as you would before making a normal purchase. By using these wordings they are creating a sense of urgency, "Buy it now!) But remember to pause, decide if the 'deal' is really a deal, check the competition's prices and look for coupons to combine with the sale for a truly good deal!