I just listened to the This American Life episode "129 cars" about a month in a car dealership - SUPER fascinating look at the industry, with a lot of insider information:
http://www.thisamericanlife.org/radio-archives/episode/513/1...
http://www.thisamericanlife.org/radio-archives/episode/513/1...
In fact, I used a lot of the knowledge from '129 cars' to help with a recent purchase of a Jeep (not from that dealership, sadly). I'm going to write up a blog post about the experience - I learned a lot and it should be helpful to others.