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Not every great idea should be copied. But thanks to NetFlix, which proved that DVDs could, indeed, be rented profitably by mail, people are now trying to rent anything and everything through the mail, with orders placed over the Internet. Purses, videogames, and now ... textbooks? Bookrenter.com is one such venue, claiming that it wants to "shift purchasing power back to students." It recently pitched Valleywag — always a dangerous sign, in and of itself — claiming to be the first textbook rental service on the Web. First, well, no. Secondly, any student who hasn't learned to scour eBay, Half.com, and a slew of online used-textbook sites deserves to be gouged by campus bookstores. Heck, most campus libraries have multiple copies of textbooks in their collections.

But what Bookrenter will learn the hard way is that a business model that works well for movies and videogames won't necessarily work well for textbooks. We asked an actual college student why, and the answers were instructive. Leave aside the sheer weight of textbooks, which drives up shipping costs. The main problem is that many textbooks are updated annually. For example, the University of Caifornia at Davis has 2,000 students taking chemistry. The required textbook costs $200, and a new edition is published, and required by teachers, every year. On top of that, the text is required over three consecutive quarters. The cost difference between a purchase and a year-long rental would be negligible. Bookrenter will wind up with a bunch of textbooks which can't be re-rented. Most importantly, students wouldn't be able to doodle in the margins.