The Public Company Accounting Oversight Board frequently raises concerns about managerial biases in fair value measurements and auditors' inability to identify such biases. This study focuses on Level 3 fair value assets, where the measurement involves a significant degree of assumptions and subjectivity. Utilizing audit hour data mandated for disclosure by South Korean audit firms, our research predicts and confirms that increased effort from audit partners effectively reduces the misvaluation of Level 3 fair value assets. Conversely, the effort exerted by lower-ranking auditors shows no significant association with fair value misvaluation. The positive impact of audit partner effort on Level 3 fair value measurement is predominantly observed in partners with lighter workloads and substantial experience in auditing Level 3 fair value instruments. We also find a similar result when using the audit-firm level fair value expertise. Furthermore, our findings indicate that the positive impact of audit partner effort on Level 3 fair value measurement is mainly observed in firms with long-standing relationships with their audit firms. These findings emphasize the critical role of oversight mechanisms in improving fair value accounting quality and highlight the crucial function of audit partners in examining complex audit areas.