"Heads up-- If Havok's position in UA #5 really upset you, it's time to drown yourself hobo piss. Seriously, do it. It's the only solution." - Rick Remender
Sucks 200 character limit.
I use LoneStar's buying system database to record my collection, mainly due to how easy it is to enter books and navigate, but I also sell my extras there. Their database is live 24 hours a day, and based on parameters they have set up for each book, you can see their buying prices rise and fall due to demand. The prices are constantly fluctuating, to the point that one day they may offer .25 for a particular book, but a few days later the price could be $2.00 or .02. The more valuable the book, there is a bigger difference in offers depending on how low their stock is. I had been using it almost a year before I caught on to the way the prices went up and down, so I sold some books for much less than I could have by waiting. By the way, I definitely recommend their database if you want to record your collection. It's a one-step entry process per book, which saves a lot of time if all your books aren't NM.