Intensive in-store use of smartphones has driven ethically questionable behaviors with significant economic repercussions for the survival of brick-and-mortar retailers. The mobile-assisted showroomer’s dilemma refers to the dilemma such shoppers experience at the moment of decision in a brick-and-mortar store, when they are holding an item in their hands, check their phone, and hesitate between buying it (a) at the physical store (loyal behavior, LB) or (b) through a cheaper online retailer (competitive behavior, CB). Using the theoretical framework of the Composite MES, this research proves that the dilemma exists: in a sample of 648 mobile-assisted showroomers, 44.91% would engage in CB vs. 55.09% in LB. Furthermore, 50.6% of the CB is explained by two dimensions of ethical judgment: relativism and egoism. To prevent sales leakage at brick-and-mortar stores, ethical judgment must be considered. The greater the weight of the relativism dimension, the less predisposed customers are toward CB. The egoism dimension is positively associated with engaging in CB. LB is a major opportunity for independent brick-and-mortar retailers.