I use the library a lot but when I buy books I almost always do it at used book sales. It's hit or miss of course but you get some rare finds, some "I've been looking for this" moments and it's amazing how often you find hardcover versions of bestsellers from only a couple years ago that people got rid of. My favorite is to go to the bag sale on the final day, books may have been picked through but I've never not come home with at least one sometimes two or three bags that I packed so tight with 20-30 books in each that they looked like some weird tetris game .........To me the "as many books as you can fit in the bag" rule is like a compliance challenge.