1) Speak with your banker, and get financing in order when you arrive at the dealership.
It varies from state to state, but in the financing "box" is where the dealership makes most of their $$. It is legal for them to arrange financing for you at say 2.5%, when the rate is really 2.3%. (they keep the remainder) That said.....they have deep channels for financing. If they can get you 2.5% and the best your banker could do was 2.7%--- you may be better off going with the dealer and giving him the points. Check with your banker first.
2) Don't buy an extended warranty, paint protection, or any other B.S. the dealer tries to sell you while in the "box". Almost all of it is B.S. or stuff you can buy for less $$ elsewhere.
3) Dealers are people too--- they need to make a decent profit to stay in business and provide their services. Asking what they have into the car is dubious.....as they may not be honest. You can safely assume that if they are asking $15.5, they have built-in cushion for profit. Since the car has been sitting for a long time (and these cars aren't selling very well) it is costing them money. Lowball them with cash (or financing) in hand. They may be very eager to unload it--- and you may get a great deal. If they balk--- walk---- there's plenty of inexpensive Abarth's out there. (and yes, the Abarth is worth the extra $ over the standard Turbo car) Call them back a few days later--- letting them know you're serious and you still want the car--- at $13K. Pretty soon they will get frustrated and offer you the best they can do. They may even let it slip on how much they REALLY have into the car.
4) Negotiate on total price----not monthly payment. If the total price is right--- the payment will be fine. It's way too easy for them to juggle numbers / rates / extras to get you into a monthly payment that seems acceptable.
5) Treat them with the same respect that you want to be treated with. These are humans, be honest but forthright. Tell them....."This is what I can do....either you can sell the car to me at this price, or not" No games, no run-around, no going back and forth to the general sales manager. If they pull that crap--- walk. As you are walking out, tell them "call me when you are ready to sell"
6) Before you head into the dealer-- get a good night's sleep, eat, and prepare yourself mentally. Depending on the dealer, you may be swimming with sharks-- you'll need to keep your wits about you. If you don't like the dealership----walk.
Repeat this mantra-----" There are plenty of Abarths out there...... I don't have to buy this particular example" Follow logic, not emotion.
and good luck!