Professor Hacker analyzes how to ethically dispose of review copies. Some highlights:

If you’ve taught for even one semester, especially if you decide what textbook to use in your class, then you are aware of the mixed blessing that is the desk/review copy. On the one hand, free (or massively discounted) books!  On the other hand, so . . . many . . . books.

A book that you paid for is, I think, fair game to re-sell, give away, or use for insulation, even you got it at a discount.  Free books—especially free books you requested, are a bit stickier.

I have heard, from sources I trust, of cases where faculty (mostly, but by no means exclusively, part-timers) explicitly use the re-selling of review copies as a revenue stream.  By this I mean requesting copies that they have no intention of using, specifically in order to re-sell ‘em.

As someone who sends out many unsolicited free copies, I agree with the following:

If you didn’t ask for the book—if a zealous marketing rep sent you a copy for free—then it’s probably safe to re-sell it or give it away.

However, if you are a legitimate reviewer or publication, I don’t agree with selling the book on eBay PRIOR TO PUBLICATION.