With a car or a motorcycle I size up the individual and find out a few things about them, then decide how to proceed.
If I do decide to let them drive the car or ride the bike, I make them hand over their drivers license, and maybe their car keys, too, for me to hold until they get back. I figure they are less likely to speed if they don't have their license on them.
If they don't trust me with their license and keys, I don't trust them with the car or bike. I have never had any bad experiences, other than turning a couple of flakes away that were probably druggies.
