When an internal auditor identifies a potential control deficiency based on a preliminary survey, such as the lack of established procedures for adding and approving new vendors, the next appropriate step is to gather more detailed information. Interviewing personnel involved in the accounts payable function allows the auditor to understand the context, confirm the accuracy of the questionnaire responses, and gain insights into the potential risks and impacts associated with the observed deficiency. This step is crucial before documenting the issue or planning further audit procedures to ensure the information is accurate and complete.

The IIA's International Standards for the Professional Practice of Internal Auditing, Standard 2201 - Planning Considerations.