Ugh. I would never sell my kids' books, as long as they were reading something I wouldn't care...and besides, I'd probably want to know why they liked them so much at age 20 or whatever, and maybe read them XD
I went to the used bookstore warehouse yesterday but there weren't any hardcover regulars...I did find a Hork-Bajir Chronicles hanging out in the fantasy section, not in the kids' section, though, and that made me kind of grin...yesss, they are more sci-fi, but someone obviously thought "cool artwork! this cannot be for teh childrens!?!11"