Legal advice, So whats to say he doesnt have a lien on the car? or if he even has the title? All transactions of large items like houses and cars are done through banks for security. He brings a copy of the title and you the cash to a bank, the bank checks the title and makes sure you essentially dont get scammed and act as the "witnessing party" during the transaction to show nobody was cheated on either end. On another note, i wont ever know Hawaiian laws, but in some states that im aware of, you can transfer titles by having both parties sign the title and then taking it to the local MVA/DMV for the switch in ownership. I would just hate to hear you purchased a car with a lien on it for 9,500 and the guy still owes or rather you now owe 4,000.
When handling sports cars, and buying them for that matter, its always best to make sure the car runs well. I would suggest testing the car yourself, and having a shop look at the car on the owners expense. Having the owner do this assures not only yourself, but all other would be buyers of the security of purchasing this vehicle.
As for knowing if its stolen or not, well you can ask your local police dept. to run the VIN located on several places on the car, most notably the driver side door, and the front window near the A pillar. If they refuse for some reason, well you can always try this,
https://www.nicb.org/theft_and_fraud_awareness/vincheck, im not sure how up to date it is, however its better then nothing at all. In the end if it is, well you're out of your money and a car, until they catch the guy, and you sue for your money back.
TL:DR
*Make sure you are provided with a bill of sale, this will be provided to the MVA/DMV
*Write down on the title the purchasing price, odometer, date of purchase, and lastly both parties signatures
*Make sure there isnt a lien on the vehicle, you can check with a bank, or the MVA/DMV
*Make sure upon the day of purchase you go to your MVA/DMV and switch the title over into your name, it will reissue the title to yourself, so the guy doesnt attempt to sell the title again and leave you in some sort of weird scam.
*Make sure your laws even allow party to party transactions, you dont want to get caught up in some sort of legal battle with the state because you did an illegal deal.
*Test the vehicle either yourself, or talk the owner into having the vehicle checked in a garage on his dime, he will or rather should do it if he wants the money, and honestly it only makes sense.
*Bringing a friend along for safety is always a good thing, bringing a weapon, though may sound extreme is understandable, especially when carrying nearly 10k.(I myself think that is a good idea, i brought one to buy car seats lol)
*Dont ever go inside peoples houses, or go to less populated areas, if he decides he wants to do the sale at his house, okay fine, but dont be lured down into his "basment office" to sign some sort of paperwork, it can all be done over the hood of the car, or in the parking lot of a restaurant.
I know Hawaiian prices on vehicles are astronomical due to its location, but id reconsider purchasing with cash if you are young. I found it much wiser to get the car i wanted by getting a loan. With nearly 10k, you can bump down the price of a car quite far, normally the value is around 200 less for every 10k on a 5 year loan. So if you wanted a 20k dollar car, you can get away with paying nearly half of the car off and only pay 200 a month on a loan for 5 years, leaving you with a newer car, as well as establishing credit to boot. All in all a good deal, though its up to you and your financial situation.
My car was 30k, my down payment was 2k, which left me with a monthly car payment of, 560 over a term of 5 years(i had it paid off in 3 1/2). My credit is now fantastic, as well as my pretty car and i was loan free at age 21, essentially setting myself up for any larger purchases in the future, IE a fucking house, and a motorcycle.