The #1 reason I have seen lately for rejected applications is debt ratio. You can have perfect credit, but if your debt ratio is over 50%, good luck!
I have learned from a few reliable sources that Porsche has 10% markup in their vehicles. They also get "marketing incentives" which most manufacturers call rebates. This stuff is kept a pretty good secret by most dealers. You cannot get both the marketing incentive and the low interest rates. I guess you have to weigh what adds up to the best total deal. Some banks are offering equity lines around 2 1/2% right now, so if you can get one of those, you are better off doing that and getting a couple grand off on the car. Of course, you have to have that kind of equity in your home......
If you live by credit, it will catch up to you and the way things are right now, too much debt is a very big reason for a lot of turn-downs.