Judgmental sampling, also known as non-statistical sampling, is a technique where the internal auditor uses their professional judgment to select a sample that they believe is most representative of the population. In this scenario, the internal auditors are choosing to review a sample of complaints from the last three months based on their professional judgment that these complaints are reflective of current marketing practices. This method is particularly useful when the auditor has specific knowledge about the population that allows them to make informed selections.
Institute of Internal Auditors (IIA) Standards: Performance Standards 2320: Analysis and Evaluation Internal Audit Manual: Sampling Techniques and Methodologies

According to the International Standards for the Professional Practice of Internal Auditing, the CAE must be kept informed of significant issues and deficiencies that are not addressed by management. Standard 2600 - Communicating the Acceptance of Risks requires the CAE to report any situation where management has accepted a level of risk that may be unacceptable to the organization. If the engagement supervisor learns that agreed-upon remedial actions have not been implemented, the CAE needs to be notified to determine further steps, ensuring that risks are managed appropriately and in alignment with the organization's risk tolerance.
This response aligns with the internal audit function's responsibility to follow up on management's corrective actions.
The IIA's International Standards for the Professional Practice of Internal Auditing, Standard 2600 - Communicating the Acceptance of Risks.

Probability-proportional-to-size (PPS) sampling, also known as monetary unit sampling, is most appropriate for measuring the total misstatement in an accounts payable ledger. This method is used to determine the likelihood of individual items being selected based on their size, with larger items having a higher probability of being selected. This is particularly useful in identifying overstatements and misstatements in financial records, such as accounts payable, where the monetary value of transactions is a critical factor.
Institute of Internal Auditors (IIA), Practice Guide - Auditing Sampling.

According to IIA guidance, when assembling an engagement team to audit a vendor, it is crucial to include internal auditors who have expertise in investigating vendor fraud. This expertise is essential for identifying and assessing fraud risks associated with the vendor and ensuring a thorough and effective audit. While proficiency in financial statement analysis and local accounting principles is valuable, the specific context of vendor fraud requires specialized knowledge in that area.
IIA Standards: 1210.A2 - Proficiency
IIA Practice Guide: Auditing Third-Party Risk Management

The most likely reason the Chief Audit Executive (CAE) decided to prepare an audit memorandum for management of the logistics department is to allow management to address the identified weakness timely. An audit memorandum serves as a formal communication that highlights the issue and provides management with the necessary details to understand and address the control weakness promptly. This approach facilitates immediate corrective action, thereby reducing the risk associated with the identified weakness.
The Institute of Internal Auditors (IIA) Standard 2420 - Quality of Communications: "Communications must be accurate, objective, clear, concise, constructive, complete, and timely." IIA Practice Guide on "Engagement Communication"