Many threads have either touched on or had using CC's for autos as their main theme in the recent past.....
My efforts finally paid off, and I thought I'd share what may have helped me convince the car dealer's business manager to let me use my First USA "double miles" VISA for the purchase of my wife's new car!!
The main problem that the dealers have is that "buyer's remorse" could set in and they'd have to deal with their purchase price being held up while the buyer disputed the purchase thru the card company. I offered to provide a check to the dealer, that they could hold (while not cashing it) in the event a dispute arose and I chose to exercise the "put" option on the card purchase.

This wasn't neccessary at the end of the day, but I believe that my offer to do so greatly reduced the reluctance of the business guy at the dealership to take credit cards.....On the other hand, the fee they pay to the card company can be worked out in terms of "sharing" the costs.

At the end of the day, we got a reasonably fair deal on a new car, and 40K air miles just by paying with a CC!!

Best wishes.