If you have books, CDs, movies, games that you want to get rid of, have you ever heard of:

https://bookscouter.com/vendors/

Put in the books ISBN (or UPC label for CDs etc) and they will tell you if anyone is buying it--if more than one place is, you can compare what each will pay and see if the public rates them well. Most of the vendors buy more than books. I only sell to places that let you print a free shipping label, pack them up with boxes I already have anyways and donate the items no one wants to buy....