<p>Influencer-brand fit is central to influencer selection, yet its impact on immediate sales in livestream commerce remains unclear. This research introduces follower-based fit (i.e., the similarity between an influencer’s followers and a brand’s target consumers) as a distinct dimension alongside the widely studied image-based fit (i.e., the alignment between an influencer’s persona and a brand’s image). Using two large-scale observational datasets, we show that follower-based fit is the dominant driver of immediate sales in livestream commerce. However, its effect is attenuated when image-based fit is high. Two experiments reveal the underlying mechanisms: the sales effect of follower-based fit is fully mediated by self-brand congruence, but this effect is impaired by high image-based fit, which shifts followers’ attribution of the influencer’s agency role from follower-serving (i.e., serve the followers’ interests) to brand-serving (i.e., serve the brand’s interests). Additional observational evidence indicates that this backfire effect does not arise in new influencer-brand partnerships but emerges and persists once partnerships become established. Our findings extend influencer‑brand fit literature and provide guidance for optimizing influencer selection strategies in livestream commerce.</p>