Round here we get hit with a 3% on any purchase, dealer or used. Its only payable at the time of transfer of ownership at the RTA (DMV) and it is calculated on sale price, or market value, whichever is higher. new cars that sell for more han $75 000 are considered "luxury vehicles" and any amount that it sells for above that threshold is taxed at 33%.
That being said, Ive never had anyone question the "$1000" i paid for any car ever. Seller always writes the amount on the registration paperwork, which you need as an official proof of sale, especially if youre buying a car that hasnt been registered in years.