a business like yours should be more careful, especially with all the previous stolen cars. no excuses to not photocopy ID, AT LEAST look at it.
stop trusting people, they will understand you have a business to run. if someone comes in for a test drive and you are closing in 10 mins tell them to come back when you have time to deal with their request without rushing and making mistakes.
and if they wanna drive it around the parking lot tell them that will not tell them anything.
i get ID'd at boston pizza for a draft beer, around the parking lot with an uninsured car imo is a lot more important.