Jebus. I heard rumors people paid interest rates that high but I've never met anyone who willingly did so. You say your rate was 12.5% with a 684 score? That seems a bit high for that score. I would have thought you needed to be in the 400's to get that kind of interest rate. Definitely hit up a credit union, your bank and then AFTER getting pre-approval numbers from those twoand deciding on a car THEN hit up the car dealership for their best competitive interest rate offer. Then when they come back with a marginally better offer go ahead and call up your bank/credit union right there on the spot and let them fight over who can give you the best deal.
Note* This is assuming you have already done the prerequisite and mandatory walk out at least once. Never. Ever. Ever buy a car without walking out of the dealership at least once. Preferably to go to another 2-3 dealerships with what they offered you and see who comes up with the better offer.