The same goes for books and DVD's. Ultimately when I buy a game, it's mine, I own it, and if I feel it wasn't worth it or it isn't worth keeping, I am perfectly at liberty to sell it back to the shop. Games are expensive enough without customers being expected to keep the duds or games with no replay value.
A game I'm developing with some friends:
www.xnagg.com/zombieasteroids/publish.htm
It is largely a technical exercise but feedback is appreciated.