If the Dealer has registered your car before you put the PIN number and you haven’t paid the AP yet, they are in a tricky situation if you refuse. They would have to sell the car at a reduce price because technically the new owner would actually be the second owner. You could negotiate a substantial amount off of your AP and a full tank of fuel if you still wanted the car and they would be happy to do that. It would be a better hit for them than making a bigger loss on a registered car with 1 owner.