I’m sure that happens but it may still be a net benefit. The original owner gets rid of a book they don’t need and don’t need money for, somebody who needs money takes the book and sells it, and somebody who wants the book buys it.

But some do seem to just have high turnover. When I moved away from a place in New Orleans I probably took about 100 books to one of these over the course of a month. Most of the time I’d come back a couple days later and find all the books I dropped gone—and entirely different (and not obviously inferior or cheaper) books in the library.

The margins on used books aren't there to make this worth anyone's time.