I believe the state of Washington has labeled it an excise tax, not a "sales" tax, so as to divorce the actual dollar amount paid from the tax. That said, I bought a nice van for 6K, it was a stripped out passenger van, no seats-when I went to register it, the lady wanted to charge me tax on a $ 12,000 vehicle. After showing her the actual ad for the van with the price listed , and the bill of sale, I was able to get a reduction to being taxed on a 8k vehicle- the point in this case was that the "blue book" van bore no resemblance to the one in question. All they have to do is get the condition wrong, or the trim level wrong, and it can increase the value hugely.