In terms of mileage, factory warranties running out, questionable histories, etc. Also, if one is listed for $20k expect to buy it out the door at $23k with tax, tags, and title. Not trying to shit on your cake or anything.. maybe I'm biased because I just bought one and seeing the depreciation on these things makes me shed a tear. If you find one cheap, it feels solid, and the title is clean go for it, but I checked on a few of the ones posted under $20k and they were in accidents.