Final answer:
Confirmation is important evidence for an auditor when there is doubt about the existence of accounts receivable. It involves requesting confirmation of balances from third parties, which helps to verify that the receivables are real and that the amounts reported are accurate.
Step-by-step explanation:
Confirmation is most likely to be a relevant form of evidence with regard to assertions about accounts receivable when the auditor has concerns about the receivables' existence. Confirmation consists of obtaining evidence from third parties to support the assertions made by management regarding the components of the financial statements. Specifically, when auditors are concerned whether the accounts receivable actually exist, confirmation can serve as a strong form of evidence. Confirming receivable balances directly with debtors can help the auditor to verify that the receivables are not only recognised but also substantiate their existence.
Confirmation is less likely to address concerns regarding valuation, classification, or completeness directly since these require additional auditing procedures and analysis. However, in the process of confirming the existence, information relevant to valuation and completeness may also be obtained, such as evidence of disputes or returns that could affect the receivable balance and indicate a need for adjustment.