I think you should go to a carmax and get their appraisal no matter what. You can then work with the dealer to get them to do better or at least match that. If they won't you can go back to carmax and sell them the car.
Current car: BMW AH3 2013 - Black Sapphire-Saddle brown-ZLL-ZPP-ZTP-ZDA-HK
Past cars: Civic, Mazda6, Accord coupe, Accord Sedan.
BMW CCA Member