How Smart Are Car Buyers?

I recently answered this question when I took my sister to buy a car at a local dealership. I researched everything insurance, invoice price, finance and dealership history. The dealer did not know I knew more about them than they did about me. I also prepared by taking a Car Buying IQ Test http://209.12.22.19/alice/cartest/. I flunked bad the first time, but I researched some more and passed with flying colors. I think we all need as much preparation as possible to beat these dealers out there. If anybody has any other tools or information that will help car shopper to be smarter please suggest them.