Social robots are increasingly used in healthcare and education, but technological gaps, fears of human replacement, and moral or social beliefs can limit their acceptance. In collaborative settings, the activities to complete may influence users' willingness to participate, raising the question of how moral and social attitudes shape human-robot interaction. This paper studies the effect of the Social Judgement Theory on social robotics to analyse which factors affect the users' willingness to complete the robot's requests. The methodology classifies the activities requested by the robot into assimilation (activities people typically accept), non-commitment (activities people usually reject) and the contrast (activities some people accept) groups. We conducted a user study with 63 participants interacting with the Mini social robot in a collaborative session where it requested some actions from the user. We analyse whether the kind of activity requested by the robot, its expressiveness, and demographic, moral, social, and robot factors influence the user behaviour. Results show that the Social Judgement Theory can be extended to social robotics since the kind of activity affects the user's willingness to complete it. Besides, the results indicate that an expressive robot convinced users more than a non-expressive robot and that participants who lied about their completed activities were more easily persuaded. We also found that participants with moderate knowledge of robotics completed more activities than those with low knowledge, and individuals with previous experience interacting with Mini were more likely to comply with its requests. However, demographic factors such as age or gender do not seem to influence robot persuasion despite previous studies suggesting they are important in human-robot collaboration.