Growing awareness of the fashion industry’s negative impact on people and the environment has led to considerable growth of the sustainable fashion market. At the same time, Black Friday purchases increase annually as the sales event develops into a global phenomenon. As sustainable fashion brands are choosing to participate in the event, many communicate their offers via the social media platform Instagram. To gain a competitive advantage and maintain their sustainable corporate images, some brands use greenwashing and/or bluewashing strategies. The first part of this study explores which strategies were employed in Instagram content posted by sustainable brands, using quantitative and qualitative content analysis. We propose a research-based model of nine greenwashing/bluewashing strategies. The second part of the study examines predictive factors for consumer evaluations of Black Friday ads by sustainable brands, using an online survey and a stepwise multiple regression analysis. Findings show that consumers’ critical attitude towards Black Friday and high ad skepticism predict positive evaluations while sustainable purchase behavior predicts negative evaluations. These insights suggest that ‘sustainable’ Black Friday campaigns may appeal to consumers who show a general concern for the environment and issues of social sustainability, but not to those who exhibit actual sustainable behavior.