How to buy a new car without getting screwed

One of the things I love about living in London is the fact that I don't own a car. I hate driving to work and I hate driving in cities even more, so the ability to walk / bike / take mass transit to work is great. Add on top of that the ability to walk / bike / take mass transit to do anything in town and you've found a place that is heaven for me. Someday, I'll have to move back to California, and that is a place where you really can't walk or take mass transit to do anything. The last time I tried to ride a bike on a regular basis there I ended up with a broken shoulder, so thats out for me. All of this means, that when my wife and I finally move back to California we'll have to buy some cars. This vide on YouTube, gives some great hints about how to avoid getting screwed by car dealerships.