Relational norms as implicit rules of conduct have vital roles for the functioning of commercial and non-commercial relationships. This research further illuminates relational norms in customer–company relationships by examining antecedents that contribute to the development of relational norms and consequences that arise after a relational transgression. To test these effects, this research conducts a study with 198 customers of a financial services provider and analyzes the data using structural equation modeling (SEM) and fuzzy-set Qualitative Comparative Analysis (fsQCA). The results of this research offer new insights into the net effects and the configurational effects of relationship-quantity factors and relationship-quality factors for the development of relational norms. In addition, the findings of this research deepen the understanding of how relational norms relate to customers' reactions to relationship transgression by demonstrating amplifier and buffer effects.