Consumers face a range of messages during online shopping or accommodation reservations that aim to speed up their decision-making process. However, there is a fine line between sales promotion messages that support consumers in making the right decision and ones that exert psychological pressure. The first goal of this paper is to review current literature on sales promotion messages that use psychological pressure, especially those relying on cognitive biases. The second goal is to present a study that measures the impact of various applications of such messages during online reservations. By using eye-tracking and electrocardiography, the authors studied the physiological signals of 12 participants, during a lab-based usability study. Based on the results, the authors propose that the inappropriate use of the sales promotion messages is not recommended for companies, as these are detrimental to the long-term loyalty of potential customers.