At this point, and after many years of experience and networking, I could very likely generate a steady livable income flipping books but that would require putting lots more time into it than I do now. However, then it becomes a job instead of a hobby and that doesn't hold much interest for me. Instead I use the hobby to fund itself. Grabbing some easy flippable spec books, scouring LCS' and antique shops for gems (which I consider fun, not work), and selling off parts of my personal collection when the value starts to outweigh my interest in holding them, etc. I take those funds and use them to buy back into the collection. This keeps it interesting for me instead of just looking to make mad stacks.