One of the most difficult parts of dealing with an upset guest is not taking his or her anger personally. If you become angry or upset yourself, this starts a vicious cycle which creates more bad feelings on both sides.
Think for a moment about a professional doctor who is a very nervous patient. As the patient becomes more nervous, the doctor understands what is happening and seems to become more calm. The doctor has learned to understand what the patient is going through and not to react with the same emotions himself.
Remember that an angry, upset person needs your help, no matter how much he is raising his voice or blaming you for this problem.