While I am a frequent shopper at Best Buy, some other game shoppers may not be and many of those people may not know that your stores now sell pre-owned games. Aside from a small section in one or two of the circulars since the inception of the used game/game trade programs at BB I haven't seen very much marketing regarding it.
If you guys want to try to take a chunk of Gamestops' business away you're going to have to do an advertising blitz to get the word out. However, this may not help due to the disproportionate numbers of some games stores are being shipped back after an apparently lengthy processing cycle.
I've noticed 7-10 copies of some older PS3/PS2/360 titles that have been sitting on the shelves since they first arrived 3-4 months ago. They include copies of Two Worlds II for PS3 and Enter The Matrix for PS2.
Unfortunately another thing that may be lagging behind is price drops on these games and even if they are implemented quickly the price tags are not always changed on the products themselves.
Moreover, Best Buy really should get their lawyers looking at how exactly Gamestop skirts local pawn laws and is able to put out traded in products immediately after taking them in. I say this because the one month or MORE turnaround time from when items are traded in till when they are finally shipped back out to stores to be resold is hurting pre-owned game sales just as much as the lack of marketing dollars being spent on it.