I have a bunch of books I don't need laying around and I consider selling them. They're good books and at a good price they'll sell like hot cakes. At the same time I'm thinking that donating them to the local library will help spread the knowledge even if I end up without the money from a sale. If you'd be in the same position, would you sell or donate?
I think it depends on the value of the books and whether or not you think you'll ever want to read them again. You have to ask yourself if money you make from selling them outweighs the effort of selling them. If you donate them to a local library, you can loan them out again yourself in the future if you ever want to read them again, too. Or the best option might just be to sell the most expensive ones and donate the rest.
A second hand book depending on it's quality sells at about half it's price or maybe less. Finding customers is no easy task too. There comes a time when you have to choose whether you'll spend more time trying to find buyers for your book [good for you if you want to get into the e-book selling industry] or spend your time elsewhere and make more than you would have made trying to sell the book. So my suggestion would, be, give the books to your library.
Honestly I usually just donate my old books because I figure I can't get that much for them anyways. With that said, if I had a book I knew I could get a decent amount of money for then I wouldn't even think twice about selling it, I could use the money to buy some new books
I would suggest to donate your books to people that you know they will read them. Give a book to them like an unexpected gift of kindness and tell them, that when they read it to pass it forward to another. That way you can share some of your experiences made by those books with others!
If you don't really need the money, then I guess it's advisable for you to donate it. But if you do need the money, then you should just sell it, at least you will help yourself if you do so.