A little bit on the process.
The dealer is in the business of profit. When you sit with the salesperson, he brings out a sheet of paper called a 3 or 4 square. It has boxes for "price", "trade", and payments. You will show the salesman(salesmanager) where your main interest are. If you spend all your time on price, they'll work the trade. If you have no trade, they'll work the payment.
The finance dept. has a 1/2 dozen or more places for your loan that are legit financial institutions, and a few less legit. The legit ones are for new and near new cars, and cater to people with good credit. New cars have warrentees, and good credit proves to them a good posibility of payoff. These Companies may have rates of 7%, and allow the dealer to add on a maximum of 1-2% Fee for which the dealer is paid by the lender. So, the finance manager quotes 9%. If that is agreeable to you, the deal is done, and the dealer gets 2% of the loan deal back. A $20k loan/+2% can net the dealer and xtra $2 grand.
If you are buying used, mileage is a big deal in the finance biz. Below 60,000 with a warrentee for the life of the loan "MAY" get you prime. However, when you get beyound the 60K mile mark, and/or under certain credit scores, you get into the other finance resourses, and rates go up, usually 12 to 19 or so. These people don't have the same kick-back limits as the prime lenders. The sky's the limit. Before you sat down, the finance guy knew who would buy his loan, and his "JOB" is to make money on this deal. Especially if you beat them out of it on the price. The finance guy adds interest on and presents it. If you sign, it a deal. The money you think you beat them out of, wheither it be price, or trade, is back in the folder. It's the way it works. They are not a non-profit organization.