WSJ.com - Analyzing Customers, Best Buy Decides Not All Are Welcome: "The devils are its worst customers. They buy products, apply for rebates, return the purchases, then buy them back at returned-merchandise discounts. They load up on 'loss leaders,' severely discounted merchandise designed to boost store traffic, then flip the goods at a profit on eBay. They slap down rock-bottom price quotes from Web sites and demand that Best Buy make good on its lowest-price pledge. 'They can wreak enormous economic havoc,' says Mr. Anderson."