I haven't researched this, but I can write a credit card check for the total purchase price of a car I'm looking at, fixed APR of 3.9 percent until paid off, with a $199 transaction fee. At first glance, this seems like a no-brainer.

Dealers will not let you do that, since they pay percentage on the transactions.
Tried it myself. They will let you do a 'down payment', however.
Also, they are trying to get you to do the financing with them..

Dealers will not let you do that, since they pay percentage on the transactions.
Tried it myself. They will let you do a 'down payment', however.
Also, they are trying to get you to do the financing with them..