For years, if Costco customers wanted to shop with a credit card, the retail giant required them to pay with an American Express card. But as of Monday, the giant big-box retailer and its 81 million customers are switching over to AmEx's rival, Visa.
Why should anybody care? Well, if you don't shop at Costco, there's probably not much reason. But, if you are one of the millions of Americans who like to buy 12-packs of paper-towel rolls or 30-pound boxes of frozen beef patties, then here's what you need to know: