I'm not sure 'miss priced' is necessarily the case- I think they're priced to move, and obviously there's no cost-of-sales, so its a volume game.

Of course one can find truly valuable stuff, not just books, but I never have...

All mispriced even means here is that it would still move at a much higher price. If the goal was just to make sure everything moves, you could price it all at zero.