Here, Instagram, Facebook marketplace. I have enough avenues that when I get books I want to move, I can move quickly, much quicker and efficiently and without incurring fees. I have a handful of people who buy keys and other stuff from me. If it is 50 cent or dollar bin stuff, I put together lots of 20-30 comics and sell them for $15-20 locally. Always some minor collector or people picking up stuff for their kids.
I just bought a 1000 book collection and moved all but 200 books or so in a couple weeks. Ebay is too slow and too expensive for me to waste time on most of the time.