It's very unfortunate that a dealer would act in such an unprofessional manner. In my opinion, all you can do now is be a squeaky wheel.
Yes you can attempt to talk with management at the dealership and work out a deal.
If you (and they) cannot come to a mutual agreement, then...
- Yes you can leave negative feedback on eBay.
- Yes you can contact eBay and let them know that a licensed dealership is not honoring the term of service of eBay (good way to get banned from the bay).
- Yes you can share your experience with the this and any other forum/venue that will listen.
And at the end of the day, you can move on and find another car and get a deal done with a reputable seller who will not make you feel like you need a shower (or worse a lawyer) after you get home with your new car.
Good luck!
Chief