The purpose of this study is to investigate how auditors are influenced by irrelevant information and minor error in client records. Also, this study investigates the role of trait skepticism in the assessment of dirty documents and the auditor's skeptical action. In the regard, this study conducts a 2 by 2 experiment to examine how auditors respond to client’ dirty documents containing irrelevant information and minor error. The statistical sample consisted of 207 auditors working in trusted audit institutions of Tehran Securities & Exchange Organization in 2019 who were selected by random sampling. To investigate hypotheses, an analysis of variance and the structural equation modeling approach were used. Results indicate that the presence of irrelevant information and minor error influence auditor’s skeptical actions. Specifically, this results suggests that the presence of irrelevant information and minor error lead to increase in sample size. This finding suggests that client dirty documents may contribute to over auditing, which is a waste of financial resources and an unnecessarily stressful misuse of audit staff. Also, Consistent with the models developed in Nelson (2009) and Hurrt et al. (2013), the results suggest that the trait professional skepticism influenced an auditor's skeptical action. The results indicate that auditors with higher levels of trait professional skepticism are more likely to take more skeptical actions when evaluating audit evidence and select a larger sample size. Furthermore, the results indicate that trait professional skepticism moderated the relationship between dirty documents and sample size. In other words, the effect of client dirty documents on the auditors' skeptical action depends on their level of trait professional skepticism.