trade in values for some games...

Okay well first off u probly dont know me cuz im always in the wii forums so yeh.Okay well i want to know if anyone knows something about Gamestop/EB games trade in values, or a better place to trade in games.i got 13 old GBA advance games i never play and want to trade in and like 5-6 Gamcube games. I checked on there site and they had some games trade in values but not all, the ones they had that i am trading in is Xd gale of darkness, super smash bros melee and DDR mario mix. It says in small letters under the prices something about prices may change or something like that. I want to know if anyone knows exact prices on GBA games and Gamecube games at Gamestop and Eb games. Or if you know of somewhere else that is good for trading in games at.