The real problem is that merchants can't state that they don't accept refunds in cases where people bought and received what they asked for but they didn't actually want the think they bought. Kind of a corner case I'd think, but one that led to the disappointment of both people in this transaction.
One problem inherent to buying books online is that you aren't always sure of their content. Google Books and previews help with this, but they aren't of all books. Sometimes you get a book and realize that it just isn't what you wanted (Oh... this book on Ruby assumes you're using 1.8.6, etc).
If the seller has a return policy that accepts it in that time, and its in good condition, then the retailer should accept it back. This is how I view it to work on Amazon anyway. Other places like eBay, it doesn't work like that, but it is known.
Order a pair of shoes from Zappos. Get them. Look at them, and then send them a return note saying, "They are exactly as I wanted, and fit perfectly, but I just realized I don't need them", and you will not get a return note about how you might have 3D scanned them.
Overall, I really feel that if you're going to sell in Amazon's house, then you've gotta act like Amazon. If not, then you should consider selling elsewhere.
As an aside, in some juristictions, customers are legally entitled to a full refund if they buy something online and within 7 days, decide they don't want it.
On Amazon if I get something (a shirt) and when I get it I realize that I simply don't really like it, I can return it and they are more than happy to take the return. Same with Zappos or other companies that are generally excellent with returns from customers. But the reason they are cool with it, is because there is a large chance you'll deal with them again. A small loss in trade of happiness for likely future purchases.
But being one of the thousands of vendors on Amazon, I'm guessing you don't have this outlook. I personally can't remember the name of a single Amazon vendor I've bought from. I only buy from them if there's either no other options, or if they are offerring significantly cheaper (even when factoring in Prime shipping, which few of them do) than Amazon themselves.
Another thing it brings up is why these companies sell books for 16 cents, or even less to begin with. Clearly, that can't be a way to make for successful business, so like sellers on eBay tried many years ago (and still some today) they are trying to make up for it on shipping fees, in order to beat out competition and likely to avoid giving Amazon a cut.
I don't think Alex is being unreasonable, given that the standards of the Amazon storefront are such that allow for such. On other storefronts, it would be less acceptable. I don't think trying to return an item in an eBay auction for example that is in perfect condition and as-described in acceptable. Yet on Amazon, it would seem to be an ok thing to do. Just as there are social norms, there are corporate norms, and being in a storefront like this carries those norms.