That's the buyer's perspective though. I buy used books as well although I'll often actually pay a premium for an eBook because I have the most reading time when I'm traveling.

But selling low cost goods as an occasional thing is incredibly time consuming for the return. In the past I sold on Ebay every now and then and basically came to the conclusion that unless I was making $50+ on a transaction it just wasn't worth the hassle. Books are easier in general but they also are usually a race to the bottom in terms of pricing.