Previously viewed DVDs are always 4 for $20 if they're $9.99 or under. the ones that are $14.99 and below are either 2 for $20 or 3 for $20, it changes every now & then. the games are probably only for those that are under a certain price and previously played. I bought GTA for 360 from blockbuster used for $14.99 and had to take it back 3 times in the span of 2 days. then I rented it from another blockbuster and swapped the disc.
also @ blockbuster for the summer, a game rental is 8.99, but for $10 you can rent any game or movie and swap it out an unlimited number of times for 7 days. 2 out at a time is $15. so if its any games you wanna play or movies you wanna watch, better hop on that.