Purpose – Cause-related marketing – linking product sales with donations to a cause – are popular with consumers because they produce warm-glow feelings (the positive route). But when they involve large donations, they may trigger consumer scepticism, reducing the warm glow (the negative route). Drawing on the elaboration likelihood model, the purpose of this paper is to examine whether large donations in cause-related marketing can produce consumer scepticism and reduce the warm-glow effect and positive attitude towards the retailer. Design/methodology/approach – An experiment varying the donation size (large, medium, small) in a cause-related marketing offer run by an office equipment retailer is set up. Hypotheses are tested using bootstrapping regression analyses. Findings – The negative route has the greater effect: scepticism towards the offer mediates the relationship between donation size and the warm glow. Furthermore, scepticism towards a large donation is higher (lower) for respondents scoring low (high) on altruism and high (low) on familiarity with cause-related marketing. Practical implications – When using cause-related marketing, retailers should choose their features and target audience carefully in order to reduce scepticism, e.g., small donations should be offered in promotions targeting consumers who are familiar with cause-related marketing and show low altruism. Originality/value – This study contributes to the recent research examining the negative effects of cause-related marketing by explicitly conceptualising and measuring scepticism towards cause-related marketing. The findings are also valuable because they indicate the importance of a shift in focus, away from the conventional question of cause-related marketing effectiveness to the more specific and under-investigated problem of the appropriate core target consumers.