The purpose of this study is to investigate the role of negative electronic word-of-mouth (N-eWOM) messages on attitudes, subjective norms, perceived behavior control (PBC), and the intention to purchase sustainable dairy products. This study also investigates the moderating role of product sustainability claims to reduce the effect of N-eWOM on customers. It comprises two experiments on college students (n = 120; 90) who have at least two accounts on different social media platforms. We use both qualitative and quantitative techniques. The model was developed and tested on data collected from questionnaires. The results of Study 1 suggest that N-eWOM reduces purchase intentions, attitudes, subjective norms, and PBC. High N-eWOM reduces purchase intention more than the low N-eWOM. Study 2 found that with high N-eWOM, product sustainability claims (congruent or incongruent) moderate the effect of N-eWOM on attitudes, subjective norms, PBC, and purchase intention. Purchase intention is higher when a product sustainability claim is congruent. These novel findings contribute to our understanding of ways to mitigate the impact of N-eWOM by taking preventive actions, such as making product sustainability claims.