Mr. Sam Hill has worked for Dr. Lee Chang for several years in the administration of De Changs medical practice. Sam demonstrates a loyalty that is rare among employees. He hasn't taken a holiday in the last three years. One of Sam's primary duties at the medical office is to open the mail and list the cheques received. He also takes cash from patients when they leave. At times it is so hectic that Sam doesn't bother with giving patients a receipt for the cash paid on their accounts. When the traffic is slow in the office Sam offers to help Ms. Mary post the patients' cash payments to the accounting records (i.e. patients' accounts receivable). She is always happy to receive Sam's help, because Sam is a very conscientious worker.

Required:

Identify (& briefly explain) any principles of internal control that may be violated in the above situation.