I've sold the ones that I really feel are taking up shelf space, but I like to keep most of my games. I got tired of being ripped off by them. Oooh, thanks for the $15 back on the game I just spent $60 less than a month ago. And that's a good trade in for them.
I think your local store is Ripping you of I normally get between $30 and $35 for Wii games within the first month, Which is what I got for Rayman RR and there was $35 for Super Paper Mario I could of took but I ebayed it and only got slightly more, plus if you are trading its best to only do it on games your preordering as you get 10% more.
I would actually prefer them to offer people less then they can sell the games for less rather than $5 off the retail price which is lame.