I’m a big fan of coupon codes, and of course there are some out there for Nintendo DS purchases. You should never pay more than you have to for used games at GameStop.com. The coupon code PPLAY15, which has been in wide use for years, takes 15 percent off the purchase of used games. It’s not good on bundles, consoles or accessories. Just type the code into the box after you put the game in your online shopping cart. Voila! Cheaper cheap games.