Tight control over keys does not eliminate the need for rigorous policies and procedures regarding test drives.
In particular, one should also have a dealer employee ride along on every demonstration and test drive. Normally that is not an issue, as the test drive is the best opportunity for a salesman to point out the features of the vehicle. The only conceivable reason for allowing customers to test a vehicle unaccompanied is if the dealership is running thin on staff during a busy promotion.
Simply put, a customer should never drive a vehicle away unaccompanied unless certain safeguards are in place:
Your dealership knows the individual from previous transactions or well-founded personal knowledge;
You have copies or his/her driver’s license and a credit card;
The person leaves behind a vehicle of equal or greater value than the one he/she is testing, and you have good reason to believe it is owned legally.