Have you considered donating them? I believe that public libraries can benefit from the proceeds of selling them should they not have a place for them in their own stacks.
In my experience, most donated books go straight to the "for sale" cart, and if not sold, are tossed straight into the dumpster. When I was younger I was a part-time janitor in a library, and every day there was another pile of books in the recycling bin for me to bring out to the bin outside. Normal public libraries don't want old books; they're busy enough clearing their shelves of books that haven't been read in ages for new stock that patrons will actually be interested in reading.
In other words, just toss them in the dumpster yourself, unless there's a particular reason you're library might be interested in them (for example, if you have a large collection of Tintin books or Bill Peet children's books in like-new condition, they will probably be interested, because those books are timeless).
I won't get rid of my technical reference books, and my 1st editions.
I have come to realize I can't waste anymore time on bad writing though.
I have way to many books, and I need to get rid of 90% of them. I just can't toss them though.