This may not be relevant... but have you taken your car to Car Max for a free appraisal? They usually come in with a strong offer (since they can sell your car in over 100 locations and will just transfer your car somewhere they can make the most from it). I've purchased many cars and I always walk in with an appraisal from Car Max to have them at least match it.
Not sure if that helps... but if you were able to show that more than one location will give you more for your ride... maybe that would help.
(Not a dealer... I've just purchased a lot of cars).