I think a lot of us participate in religions that mandate not taking things you haven't paid for. For those who don't have a formal religion that mandates it, many still have a personal moral code that does.
Or even you've read that horrible story (think it was by O. Henry) about all the tragedies that arise after a cashier gives back more change than she should have, and the customer doesn't tell her, even though he notices. That'll make anyone paranoid about making someone's till not balance.
My cousin's memoir of love and loneliness while raising a child with multiple disabilities will be out on Amazon soon! Know the Night, by Maria Mutch, has been called "full of hope, light, and companionship for surviving the small hours of the night."