A large portion of audit evidence is gathered through inspection of documents and records. External documents, documents that are generated outside of the organization, provide more reliable evidence than documents generated and maintained at the client. 

Required: 

a. For each of the documents below, indicate if the document is a strictly external document (obtained from an external party), an external-internal document (generated outside of the organization but given to the auditor by the client), or an internal document (generated and maintained by client).

1. Receiving report. 

2. Customer purchase order. 

3. Bank statements received directly from the bank. 

4. Copies of sales invoices. 

5. Utility bill. 

6. Departmental budget. 

7. Insurance policy. 

8. Remittance advice. 

b. Why are external documents considered more reliable evidence than internal documents? What aspects of internal documents would help to increase their reliability?