Can the dealership re-negotiate the terms of my vehicle purchase a week later?

I am answering this on my cell. So please excuse any typos. This is called yo-yo delivery. It is not legal in some states, but it is legal in Arizona. Your contract (the long one with interest rates) will have this contingency in both front and back. Dealers sometimes use this to make you sign new contract with increased profit. It is hard to tell what is truky going on. Your best response is to ask the dealer to cancel the contract and give your money back. As long as you did not sign any separate document stating you will pay mileage or use fee, you should get all of your down payment back. And you should try to communicate via email so you have written proof. Good luck.

That's actually very common. When you leave the dealership your loan is not complete, they shop it around for approval based on the terms they think they can get. Again, while it doesn't seem right, it's a very common practice in the automotive industry.