The used game kiosks were provided by a company called E-play. Today, however, E-play suspended its operations, and consequently, both of the big box retailers have decided not to bother with the used business for now.
Analysts have repeatedly stated that the used games test at retailers like Wal-mart would basically have zero impact on GameStop.
Gamers, how do you dispose of your old video games?
Wal-mart, Best Buy Quit Short-Lived Used Games Test [Industry Gamers via Kotaku]