You bought the automobile and THEN discovered the paint defect?
I would imagine that you had ample time to inspect the automobile before purchase, it was an obvious defect - not something like you took it home and the main bearings gave out - your claim would be utterly incredulous!
You claim that you discovered the damage within a week, who's to say that you didn't do it?
If I had to choose sides, I think I would rather be the guy that sold it to you.
What section of the UCC would you even attempt to invoke?
Just for a minute, imagine yourself a neutral third party - dolly back - get a good view of the situation.
You: "Hello, I bought this car more than a week ago, and now the paint is scratched - I want my money back"
Car dealer: Blank
Your job: fill in the blank.
Your real problem: You don't want the car (it's trite but true - buyer's remorse)
Your solution: You should have thought of that before you bought it.
Get a grip,
wtd