Do people like these keyboards?
Uh. Have you looked around here at all, or did you just come straight here and post? lol
A lot of us like them, myself included. It depends a bit on the model, but most of them are pretty highly regarded.
Unused as in new-in-box and never opened, you'd probably be able to get quite a bit for it from a proper enthusiast. Again, it depends on what kind of Model M.
Welcome to GeekHack.
999!