I don't mean why they're expensive in general, or the existence of cheap 'international' editions. I mean the same book in the same condition being sold by two different retailers on Amazon or Abe Books or some other place with many times difference in price. So, for example, I was looking up Vallado's Fundamentals of Astrodynamics and its price on Amazon for a new copy varies from 100 GBP to 300 GBP. A used copy on Abe Books goes for 40 USD to 1000 (!) USD. (admittedly, 1st vs 3rd edition, but e.g.a new 4th edition goes for a 100 bucks) http://www.abebooks.com/servlet/SearchResults?an=Vallado&sts=t&tn=astrodynamics I want to know what is the rationale behind trying to sell a book for a grand or otherwise significantly overpriced. Do they include 70 virgins in the more pricey deals? Do some people have so much money that they buy the most expensive copy just because? Is this a front for drug dealing or something similarly illicit? Does it mean I can start selling my textbooks for twenty times the price I got them for and still find some buyers?