My usually habit is to buy the book, read it, then give it to a newbie here on the forum. My hope is they will read it, and pass it on as well, though they are under no obligation to do so.
There are many who like to keep their books for re-reading/research later, so most likely their books are going to remain in their well-stocked financial libraries.
Personally I don't have the room to keep all the books I've read, and honestly I seldom re-read a book. Once I've read one, it holds little interest for me. Non-fiction books get stale pretty quickly, though many authors will update and re-release their books.
You can find most any book discussed here on amazon.con, and after a bit used editions will start to show, at a sometimes generous discount.
Lately I've cut my book expenses deeply by just using my local library. I've read that some libraries are willing to add a book if requested, though I've never requested one myself.
Sam I Am
A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. Douglas Adams