Last week my computer died, which, while inconvenient, was not totally unexpected. We bought a new one on Friday night at Office Depot. Sunday morning my husband was looking through the ads and found the same computer for $50 less on sale at Office Depot.
Today, I returned to the store with the receipt and was given a $54.75 refund for the difference between what I paid and what the sale price is this week. (The other $4.75 was refunded tax.) The clerk told me that they have a 14 day window where you can receive a refund for the difference if it is advertised as cheaper.
Make sure to check the ads after a major purchase; you may be able to get a refund if it goes on sale shortly thereafter.