I'm sure you're very trustworthy

A man comes in to the store that I don't know at all. He's not a regular customer, family or friends of any of the staff or even a neighbour....

Customer: Can I just take this book now and come back later and pay for it?
Me: Umm sorry no.
Customer: But I'll come back later this afternoon I promise.
Me: We really can't allow merchandise to leave without it being paid for.
Customer: I'm trustworthy. Don't I look like I'm trustworthy?
Me: You look very trustworthy sir but I'm afraid it doesn't really matter what I think. We can't allow you to leave with a book that hasn't been paid for.
Customer: Okay, I guess I'll pay for it then.
Me: Okay.

Strange don't you think?