rain check

Rain checks keep customers from defecting to the competition. Some states require stores to make good on their advertised offers by providing rain checks, because when a store advertises an item on sale, it is expected to have that item in stock. If rain checks didn't exist, stores could run ads for cheap items and never have to honor the offers. (Unfortunately, this rule often doesn't apply to auto dealers.) In some cases, vendors must print the words "No Rain Checks" in their advertisements if the stock is truly limited, putting customers on notice.