Amazon has long enjoyed an unbeatable price advantage over its physical rivals. When I buy a $1,000 laptop from Wal-Mart, the company is required to collect local sales tax from me, so I pay almost $1,100 at checkout. In most states, Amazon is exempt from that rule. According to a 1992 Supreme Court ruling, only firms with a physical presence in a state are required to collect taxes from residents. Technically, when I buy a $1,000 laptop from Amazon, I’m supposed to pay a $100 “use tax” when I file my annual return with my home state of California. But nobody does that. For most people, then, most items at Amazon are significantly cheaper than the same, identically priced items at other stores. Read the full story at Slate.