Basically, if you're shopping for rock bottom price, you can't pay with credit. If any dealer is willing to let you charge the full amount of the car to your CC, then you are not getting a good deal and should instead negotiate a lower price of the car. A better price should be worth more than the miles you earn. I'm sure any dealer would gladly allow you to pay with a credit card as long as you pay the 2-3% transaction fee.