Start a blog about that car. Write about the purchase process - why you want the car, where you went to look at it, what your family says about it, what friends say about it, what reviews say about it.
Document everything as you look for/buy the car you want and blog it.
Set up advertising for blog.
Buy car.
Document car experience after the sale.
Write off car. Your blog is for profit. You have adsense, etc on it - there's your proof. You had to buy the car or you wouldn't have any credibility as an expert on it. Your business hinges on your credibility as an owner, etc.
hahaha. Yeah, and do the same when you buy a new house as well. Oh and start a food review website, write off all your food. Or just one big review website that documents everything you spend money on and write it all off.