More than 100 popular titles will supposedly fetch $20, with many others valued for less. Joystiq notes that the store offers an online estimator, but it may not offer the most fair or accurate number. For instance, Alpha Protocol is priced at $27, while Mass Effect 2 is only $8.
Best Buy's move comes at an awkward point in the used games market. Many studios have been criticizing the practice of reselling games and are developing measures to profit from second-hand sales. It's also worth mentioning that GameStop recently said it disliked being in the used games business, while just yesterday, Target announced a similar exchange program for games and other electronics.