It seems that sales tax gets applied to the agreed upon purchase price of the vehicle, but can it be calculated on the cost of the vehicle after your trade-in equity has been applied. So for example. If the dealer and I agree upon a purchase price of 20000, and I've got 9k in trade in equity, would sales tax apply to $11,000 or $20,000? If applied to the higher, how many of you have been succesful negotiating the lower (or can it be done?)