They were on the "sale" table at the local library for 50 cents each.
I'm guessing there's 3 criteria for getting on that table.
1. Some one's used the book like a soccer ball.
2. x numbers of years have passed without anyone trying to withdraw the book.
3. The book has been replaced with a newer imprinting.
I don't think any one ever withdrew Bedwetter, considering the pristine condition it was in when I found it where I found it.