I inherited my mother's book collection over 30 boxes worth. I went through every book writing down all ISBN numbers I found. You can look the ISBN up online to see if the book is worth selling.
I looked into selling on Amazon and I am too busy to focus my attention being a seller. Craigslist is also an option like Suntydt mentioned.
Some book collectors and stores will buy rare and 1st editions.
I donated my encyclopedias and reference books to my local library.
I know some places you can receive store credit for books. If you are wanting money, I would do your research and don't rush.
Call around your area for book sellers, dealers and bookstores.
Below are links to sites that have helped me-
Your books will have some value, although depending on the book, maybe not a lot. Your encyclopedia likely have no value. There are countless posts on this site from people who wish to sell them, and unless they are over 100 years old, usually you can't give them away.
If you have barcodes on the books you can look them up on Amazon and sell them there. The listing will also have other sellers with the same book for sale the condition they rate their book and what they are asking as a selling price. This is an easy way to see if your book has value. If you don't have a bar code you can still try Amazon but it may take more searching to find exactly what you have.
Another option is Craigslist. A third option is PaperbackSwap.com.
On PaperbackSwap you can list your books and people don't buy them they request them. You pay for shipping the book and then, once the book is received, you get a credit. With this credit you can request books for yourself and they cost you nothing but the credit.
If you aren't into books (including audio books) you can join SwapaCD or SwapaDVD and transfer your credits from the PaperbackSwap site to the other Swapa site to pick out items on those sites to b sent to you.
I'm sure there are other sites you could possibly sell on but I am not familiar with them. What you can do is go to Google or Bing and do a search for a title you ant to sell and see if a site pops up that may have your book and allow you to sell yours.
Your other option is just to pack everything up and try a used bookstore.
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