Vendor invoice) more reliable than internal (i.e. Internal evidence better when prepared under good internal control. External better when received directly from external source, rather than from client. How does documentation differ from physical examination? D. Observation: Observation relates to observing client activities; e.g., observing client personnel perform their assigned duties in the study and evaluation of internal control. Discussion: In Chapter 21, we will discuss the process of inventory observation. Is this observation or examination? E. Inquiries of Client – written or oral representations from client.