As mentioned already on here, always be very careful to make sure the keys are always under your control. Over 20 years ago, a friend's father was dealing in sports cars from home. He had a very nice Alfa for sale. Two blokes came to view it and went on a test drive - friend's father driving. They stopped so one of the 'buyers' could have a drive. Friend's father was out of the car before the other two, they quickly closed both doors and locked them from inside. Never saw the car again, very expensive lesson.
