Unfortunately the burden of proof is on you at this point.

About a year ago I took a ride with a friend of mine to pick up his new Caymen S. When we arrived they had the car out in the parking lot. It was sitting directly in the sun. My buddy took a quick look over and was satisfied. I said to him, do yourself a favor and ask them to drive it inside the garage for a minute so you can look at it without the sun glaring all over the place. Sure enough we found 2 scratches and a door ding. You would be surprised what you see with indoor lighting compared to being outside.

This is the way you have to deal with picking up a car these days. Don't be in a rush and take you time looking over your purchase.