Always ask to see the buyer's driver's license. Write down the information, or take a photo of the license.
Never let someone test drive alone--you may never see it again.
Choose a good test route that will bring out the best in your vehicle.
Never let the potential buyer drive recklessly--if he/she has an accident, your insurance has to pay.
Never let a buyer behind the wheel if you think they may be under the influence of drugs or alcohol.
Have repair and service records available.
Be pleasant and helpful.