When should I trace instead of vouch in a CPA AUD cycle question?

Use the direction of the test.

Tracing usually starts with source evidence and follows it into the accounting records. It is helpful for completeness because you are asking whether something that happened made it into the books. For example, tracing shipping documents to the sales journal can test whether shipments were recorded.

Vouching usually starts with the recorded accounting population and moves backward to supporting evidence. It is helpful for occurrence or existence because you are asking whether recorded items are valid. For example, vouching recorded sales to customer orders and shipping documents can test whether sales actually occurred.

A quick exam prompt:

• If the risk is "missing," think trace.
• If the risk is "recorded but may not be valid," think vouch.