I've got a (small-compared-to-Amazon) online bookstore, and publisher's discounts to retailers like me generally range from 30-50%. I imagine that Amazon, with

I've got a (small-compared-to-Amazon) online bookstore, and publisher's discounts to retailers like me generally range from 30-50%. I imagine that Amazon, with their volumes, gets more favorable terms. Supposing they get a 50% discount from the publisher in this case-- I imagine they are getting more, but bear with me-- that means that they are making $3 on the book, net postage (since they charge the customer a separate fee to cover the postage and handling). $3/sale is not a lot, but multiplied by X million, it adds up. O'Reilly survives because as a publisher, they are making money on every book sold, whether you buy it directly from them or through a retailer. Their direct retail sales are just a sideline.