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.
Reference:
Institute of Internal Auditors (IIA) Standards: Performance Standards 2320: Analysis and Evaluation Internal Audit Manual: Sampling Techniques and Methodologies