Wal Mart is the only place I can think of that will exchange it.
I tried to trade a sealed game at GameStop. They wouldn't give me HALF of what it was worth. Only $13.00 (for a $40 game) I ended up selling it on Ebay. Didn't take a loss. On Wii games, you almost never take a loss, even with used games.
Wal Mart didn't have this game at the time, or I would have taken it there. I WOULD actually like to have Cooking Mamma. (I'm a dork.. yes, I know.. lol) But I just don't have the money for another game right now.