title_body: Is there any way to get a discounted ebook if I already have the book?
upvoted_answer: This would depend on the publisher, and as you mention, it's difficult to prove that you bought the book unless you bought it directly from the publisher and they have a record of it. Many publishers will offer discounts if you're buying both the ebook version and the print version, so it doesn't hurt to ask if you've bought directly from a publisher, but if it's from a retailer it's less likely.