In the continuing saga of how buying and selling on the Net is getting seriously weird (怪诞 的，不可思议的), the latest chapter puts power in the hands of sellers. This is a surprising turn—the Net has mostly been an advantage to customers—and we can expect buyers to strike back with surprises of their own, may even with political surprise, because some of this is going to make people mad. (21) You remember yield management: The airlines figured it out in the mid-80s as a way of extracting maximum revenue from every flight, building giant computer systems that constantly adjust prices based on demand and other market conditions. Yield management is why you can call an airline for a fare. the mil back an hour later and the fare will be different. (22) The premise (前提) of yield management is that a particular seat on a particular flight is highly perishable; once a flight takes off with an unsold seat, you can never sell the seat. So you’d better sell it in time and price it right. Hotel executives quickly saw that hotel rooms are similar, so they adopted elaborate yield management systems. Soon conventional wisdom held that this was a terrific way to maximize revenue when selling services. Airline flights and hotel nights can be priced this way not because they’re services but because they’re perishable. Of course there are lots of goods that are perishable, so why don’t yield management techniques work on them They do—in theory. The problem is practical. Consider one of the largest categories of perishable products: clothing. (23) It’s perishable because when it’s manufactured, it’s in fashion (or supposed to be), but eventually it won’t be, so you need to sell it before it turns uncool (不时髦的). Thing is, a big store may stock tens of thousands of different clothing items. To do yield management, you have to work up an elaborate mathematical model of how each product performs in the market. Airlines sell only a few products (classes of seats); the thousands of flight segments, they handle involve less complex algorithms (数学用语；算法), or so they tell me. (24) Retailers faced the massive computational challenge of developing models for all their products and then counting all the numbers every night so they’d know how to price everything the next day. For years they just couldn’t do it economically. Now they can, as computing power and storage get cheaper. Today, if you shop at Macy’s or any of the several other retail chains, you may well be paying a price that came from large-scale computer models created by Ph. D. mathematicians and physicists. These companies happen to be clients of TSI, a Cambridge, Mass, out fit that develops pricing models for retailer clients. What’s important about this technology is where it leads. Macy’s won’t reprise merchandise in its stores more than once a day, but on the Wed every price can be reset for every customer. (25) Since each transaction is private, you generally don’t know what others are paying; nor do other shoppers know what you’re paying. So the model can update prices continually to maximize gross margin.