Unlike a physical book, you cannot truly "return" digital data. When you return a physical book, you no longer have it. With an e-book, once the file is downloaded to your device, the seller has no foolproof way to ensure you haven't made a copy, stripped the DRM (Digital Rights Management), or already finished reading it.

E-books are short enough that a fast reader could finish one in a few hours. Retailers worry that a loose refund policy would essentially turn their store into a free library, where users buy, read, and "return" books repeatedly, depriving authors of their royalties.