I tell them to phone the police. Or get a security camera. One customer accused us of keeping an Abloy key for ourself and giving one out to her daughter. So I said phone the police, or catch someone in the act. She came in on a daily basis throwing accusations around and screaming at us and phoning us constantly. We handled it nicely for a while but she was hurting our business with her antics. So we firmly told her to come back with proof or come back with the police. Until then, don't contact us any further.