I have to differ with the above approach. I would be very straight forward and business like. I need to see a valid ID, driver's license, passport, state ID (in even to no driver's license). If he has a problem with it or hesitates walk away.
These things don't always turn out great. Someone in my family married someone they met online two years ago. They are getting a divorce. There was much more to his past then he let on.
Be very careful.
Kathy
I agree with this. If he is upset by your request, he is not a respectful guy.
