<p>This study investigates the role of loyalty programs in promoting the circular economy and sustainable consumption within second-hand markets, focusing on the clothing and electronics sectors. With growing environmental concerns driving a resurgence in second-hand shopping, the study examines how marketing strategies, especially loyalty programs, can enhance consumer engagement in these markets. The study comprises two high-powered online experiments conducted with Western European participants. Participants were exposed to different loyalty program scenarios: a classic reward system for purchases, an integrated reward system for purchases and donations, and a control group with no loyalty program. The findings reveal that while loyalty programs significantly enhance the intention to repurchase, they can paradoxically decrease the intention to donate, potentially undermining intrinsic prosocial motivations. The findings underscore the need for a balanced approach in implementing loyalty programs to foster both repurchasing and prosocial behaviours, ultimately supporting the transition to a more sustainable economy.</p>