I’m just chiming in to wish you luck.
I don’t think there is a magic number you can get off MSRP. There are a lot of factors at play, almost none of which you have control. It is a major plus that you are ready to do something and not just a tiresome tire kicker. On 5he other hand, your only real negotiating power is your ability to leave and buy a car somewhere else.
If you really want the car, and the warranty hasn’t been punched I would offer 20% off and go from there. The response will depend on the salesperson’s mood that day, the manager’s mood that day, what else the dealership has going on that week, ... The only way to find out where you stand is to negotiate. Some people are better at this than others. Keep a smile, keep it friendly and ask for as much as you can off without being a jerk. But don’t be shy about wanting a deal.
At this point, a 2018 is effectively a used car. They know that, you know that... in the end money talks, bs walks. If they think you are a real buyer they will sharpen their pencil and not let you leave without a deal. Well, that’s my experience.
FYI, ignore their first expression of “no”, it’s theatre
. I’ve never bought a car without being told “ no way” first....but then, it happens...