I serve on the board of an incorporated library and until just recently was the board president.
We have a book sale room that is about 250 square feet of well lit, clean dry space in our basement with an exterior entrance. We make a few hundred bucks a year from selling books from the sale room. A volunteer staffs the book sale room and organizes, shelves and prices the books. Even with the book sale room, which is open anytime the library is open, we have to throw out hundreds of books a year. It's not worth it to give them away. The local thrift shops and good wills mostly don't want more books.
The space would better serve the community if it were made into a maker space or turned into a classroom for special programs. We could make the entire year of book sale revenue with one by donation 4 week class.
One of the biggest tasks our librarians have is culling books. We are small and it does not serve our community if we keep books on the shelves that haven't been checked out in 15 years.