A friend mentioned the other day that he’d recently made a significant kitchen appliance purchase online with a large retailer, and the next week he received an email from the same retailer promoting the appliance for $300 less than what he paid for it. So he called customer services and asked for the discount. The retailer complied (which made him happy), but it made us wonder: what if he never knew about the discount? Would he have been any worse off? How many other customers did....