I sell books on both Ebay and
Amazon. Advantages of Amazon are that you don't have to take a photo or write up a long description--Amazon uses stock photos, and you just write up a very brief (no more than 200 characters) description. You can set any price you want, and I can generally get double the price on Amazon for out-of-print books that I can get on Ebay. Listing on Amazon is free! Listings expire in 60 days but you can relist for free indefinitely. Plus Amazon automatically charges the buyer's credit card for all purchases, so the seller does not have to wait to be paid or email an invoice like you have to do with Ebay.
Disadvantages are that there are lots of penny sellers on Amazon (common books sell for next to nothing) and that books can take a long time to sell. Once a book sells, the selling fee is fairly high (15% plus 99 cents if you don't have a Pro Merchant account, which costs 40 bucks a month. If you do have a Pro Merchant account, the selling fee is 15% only). Amazon only reimburses the seller $2.26 for mailing any size book (although they charge the buyer $3.50 for shipping) and this doesn't always cover costs. You can only list books with ISBN numbers on Amazon Marketplace--older books without ISBNs have to be sold through Amazon Zshops, which are really DEAD as far as sales (because they're not searched by the Book search engine on Amazon), plus you have to be a Pro Merchant (and pay a $40/month fee) to sell on Zshops.
A final disadvantage is that Amazon has instituted a new feedback system in which buyers can rate a seller any way they please, but seller feedback for the buyer doesn't get counted in the buyer's feedback rating at all! Many Amazon buyers are relative newbies to buying on the net, and will give negative feedback to problems completely outside of the seller's control, for instance the shipping fee (set by Amazon) or the length of time it takes for the USPS to deliver media mail.
Amazon is still my favorite place to sell, despite some of the drawbacks, because it's so fast to list books there, and when they do sell, they generally sell for more $$ than on Ebay.