The fashion industry is increasingly being studied for its environmental impact, particularly concerning textile waste. In response, the circular economy business model has gained visibility, with secondhand fashion emerging as a popular solution. The rise of online secondhand platforms, facilitated by digitalization, has made secondhand shopping more accessible. However, this convenience may also lead to consumption patterns like those seen in fast fashion. This study investigates how the growing popularity of online secondhand fashion influence consumer behavior, aiming to determine whether these platforms genuinely promote sustainable consumption or inadvertently encourage unsustainable consumption patterns. Employing a qualitative methodology, in-depth interviews were conducted with active users of online secondhand marketplaces. Findings reveal the complex nature of online secondhand fashion. While online secondhand fashion contributes positively to sustainability efforts by extending product life cycles and offering consumers easy and accessible ways to support sustainable consumption practices, it also raises patterns that lead to unsustainable consumption habits. These insights contribute to a deeper understanding of consumer behavior in the context of sustainable fashion and suggest that while online secondhand platforms have the potential to support sustainable consumption, they may also facilitate patterns that undermine sustainability.