The commission policy of the client is as follows: For sales greater than $75,000, commission is 3.75% For sales greater than $50,000, but less than $75,000, commission is 2.5% For sales greater than $25,000, but less than $50,000, commission is 1.25% For sales less than $25,000, commission is 0.5%

Why would an auditor choose to examine relationships between sales and commissions? What is another way to gather evidence about the occurrence and completeness of commissions expense?