When internal controls are weak, it is important for the auditor to rely less on the internal controls and instead perform more substantive testing. Detail testing involves examining a larger number of individual transactions or balances to gather sufficient evidence about the accuracy and completeness of financial records. This method is appropriate because it does not rely on the effectiveness of internal controls, which are known to be weak in this scenario. Reference:
The IIA's Standards and Practice Advisories, specifically focusing on audit procedures and responses to weak internal controls.