Before you donate, read this list.
1. Library Bookstores (aka the "Friends of [insert library name here]") are run by volunteers, who are mostly retired women, and so they will save the books they like.
2. Which is why if you have technical books (software guides, radio technology, auto repair, electronics, old science textbooks, etc.) DO NOT DONATE them unless it is a science-oriented library bookstore. Try to sell them on Craigslist or eBay, even if for pennies on the dollar because.....
3. Anything the Chief Volunteer does not like will get tossed either into a garbage dumpster or a recycling dumpster, depending on the site. I have personally seen entire years of binders of Trains magazine chucked in a dumpster.
4. The Chief Volunteer will say "Those books won't sell" but it's just fear of anything new to them. The staff will conduct purges of books that haven't sold in months, even though many of the new books are just different editions of the books they threw away.
5. The entire project is a weird attempt to punish books for not being popular enough with the sort of audience that goes to bi-monthly Bookstore sales, i.e., other geezers.
6. Some "Friends of" Bookstores have tiny staffs and are open to the public five days a week, others are reliant on the bi-monthly weekend sales, the Main Branch of any library will have the best store, which is run every day of the week. However, the junking of books still takes place. Some of the books wind up donated to prisons (as with the lesser Bookstores), but a lot of it winds up in a dumpster.
7. Did I mention that the staffs can be completely insane? Some places are run by people who have been there for years, and there are zillions of hidden rules. Certain staffs have gotten it down to the point where they are nearly non-verbal, and woe betide the outsider.