Review-based control charts that combine online review mining with traditional control charts are emerging as a new tool for quality monitoring. Although previous studies have provided successful examples of the review-based control chart, the natural characteristics of user-generated reviews and their impact on the chart have received less attention so far. After briefly surveying existing approaches, this paper presents a case study of two hotels in Korea to demonstrate the potential issues and challenges faced by review-based control charts because of the characteristics of online customer reviews. The results show that a small, inconsistent number of reviews and their uncontrollable contents poses the main challenge for the review-based control chart. Future research directions are discussed based on the results.