During a discussion, one auditor noted that her approach to testing sales transactions was to select a random sample of recorded sales and trace back through the system to supporting documents, noting that all items billed were shipped and were invoiced at correct prices. She stated that she then had good confidence about the correctness of the sales account, and thus having performed a dual-purpose test, the remaining work on sales (assuming the procedures also evidenced the working of control procedures) could be limited.
A second auditor disagreed. Her approach was to select evidence of shipments, such as pre numbered shipping documents, and then trace forward through the system to the actual invoice, noting the existence of control procedures and the correctness of the invoice processing. If no exceptions were noted, however, she agreed with the first auditor that the remaining audit work on the sales account could be limited.

Required
a. Which auditor is right, or are both right? Explain.
b. What assertion is tested by the second auditor?
c. What is a dual-purpose test? Explain why the tests performed by both of the auditors would or would not be considered dual-purpose tests.