In theory, leaving money in books isn’t such a bad idea. (What kind of thief is going to wipe your shelves clean?)
Unless your younger cousin comes over, wants to read, and finds money in a book you own.
This happened to me today. I’m not denying it.
In fact I was the one who recommended the book to him. That was before I knew I left ten dollars in there.
Now I’m ten dollars poorer.
And this is why I don’t donate or give my babies away.