When Skeptics Believe: How Proactive Sustainability Signals Build Brand Loyalty

When brands back sustainability claims with real investment, measurable targets, and third-party verification—what we term proactive sustainability strategy (PSS)—do consumers reward them with loyalty? We address this question through a serial mediation framework. Signaling theory grounds our core prediction: PSS should first enhance perceived authenticity, then foster trust, then create value—a chain that ends in loyalty (H1–H2). Skeptical consumers, we argue, should respond more strongly—not less—to credible PSS signals (H3). Three experimental studies provide converging support. Studies 1 (N = 60) and 2 (N = 251) validate the experimental materials and test the complete theoretical model using a fictional skincare brand, confirming the serial mediation pathway (indirect effect = 0.073, 95% CI [0.042, 0.113]) and significant skepticism moderation (b = 0.23, p = .027). Study 3 (N = 280) extends these findings with a four-condition signal decomposition design incorporating incentive-compatible behavioral measures: the bundled PSS configuration outperforms third-party certification alone (d = 1.20, p < .001) and generates a 34.8% price premium over a no-signal baseline via BDM auction, with 88.6% brand choice rates versus 28.6% at baseline. These findings offer theoretical contributions to sustainability marketing literature and practical guidance for brands seeking to build authentic connections with increasingly discerning consumers.