Developing policies and procedures for the internal audit activity is the most effective way for the chief audit executive (CAE) to ensure that internal auditors demonstrate due professional care. This action provides a framework and guidelines that direct auditors on how to perform their duties in accordance with the highest standards of audit practice, including adherence to ethical and professional standards set out by bodies such as the IIA.References: IIA Standard 1300 - Quality Assurance and Improvement Program

According to IIA guidance, due professional care means that internal auditors must apply the care and skill expected of a reasonably prudent and competent internal auditor. This involves considering the cost of assurance in relation to potential benefits and exercising judgment and care in accordance with the complexity of the task. It does not imply an exhaustive review of all transactions or guarantees that all significant risks will be identified or that fraud does not exist.References: The Institute of Internal Auditors (IIA) - International Standards for the Professional Practice of Internal Auditing, specifically those related to due professional care.