Each country has some law about selling/trading cars if the company is directly telling you that you can buy their cars using bitcoin much better and no hassle but if you cant you have to find a person who is willing to go for a trade using your bitcoin. I still think you have to spend fiat for paying fees and working thru the contract needed.
Certainly, you have to pay through fiat for shipping fee perhaps. However, sometimes sellers would include the shipping with with through your bitcoin payment. Whenever doing this transaction, I can't do it online since I can't acsertain if I would really get the car or not, regardless it was sold in a site. If I'll do trading my bitcoin to a car, I'll do it by meet ups so that I can assure that the car is in a good condition and I can get it as I paid for it.