In contemporary business environments, authenticity is in increasingly high demand. In this chapter, we investigate the role of authenticity as consistency between an entity’s internal values and external expressions in the strategic choices of social media influencers (SMIs) within the fashion industry regarding sustainability-focused collaborations. After a theoretical background, this chapter focuses on the perceptions of green micro-influencers directly involved in sustainable fashion brand partnerships operating on Instagram to understand how their internal values align with their external collaborations. Listening to their voices shows that influencers prioritize partnerships with brands whose sustainability practices resonate with their personal and public personas, ensuring consistency between their declared values and actual endorsements. This authenticity perspective fosters their followers’ trust and loyalty and enhances the influencers’ effectiveness in promoting sustainable practices in the fashion industry. Overall, the chapter contributes to the existing literature by elucidating how authenticity as consistency shapes influencer marketing and strategic collaborations.