Recently there have been a number of posts on various blogs discussing whether or not it will ever be possible for a second hand market in ebooks to ever come about, and the general consensus seems to be that it can’t happen – Or at least, not legally.
An ebook is not a physical object.
Unlike a paper book, which is a discrete and tangible object, an ebook is no more than a lot of computer code arranged in a useful fashion, so is not tangible. You can hold a paper book in your hand; try doing that with an ebook.
So the argument runs, if you sell your paper book to someone, you no longer have the book in your possession, and can only sell it once. In the case of an ebook, as it is nothing more than computer code, if you copy it to sell it, you retain the original code in your computer or ereader, and thus still have possession of the ebook. And there is no way currently to know if you have sold your only copy or made a copy before selling it.
For the publisher, book seller and author, the sale of a second hand paper book represents the possible loss of one sale; the sale of second hand ebooks represents – potentially – the loss of many sales.
A simple situation in fact.