The rise of social media influencers (SMIs) has revolutionized marketing strategies. Unlike traditional celebrity endorsements, SMI marketing leverages the influence of individuals with a dedicated following on platforms like TikTok and Instagram. Spending on influencer marketing has exploded, reaching approximately $21.1 billion in 2023. Consumers are increasingly receptive to recommendations from SMIs, especially those specializing in niche areas. This study addresses the gap in understanding how influencer credibility impacts consumer trust and subsequently, their urge to buy impulsively (UBI). It examines the moderating role of persuasion knowledge (consumers’ awareness of persuasive tactics) and the mediating role of product affection (positive feelings towards a product). The study integrates signaling theory, which explains how influencers transmit credibility signals, and the SOR model, illustrating how stimuli (credibility signals) influence organism (trust, product affection) and response (UBI). This research contributes by (1) integrating signaling theory and the SOR framework in influencer marketing; (2) examining the impact of communication factors (influencer, message, and media credibility) on trust; (3) analyzing the role of trust and product affection in purchase decisions; and (4) exploring the moderating effect of persuasion knowledge on influencer marketing's effectiveness.

The literature on influencer marketing reveals three main research streams: (1) identifying desirable influencer traits for effective brand promotion; (2) exploring the negative impacts of SMIs; and (3) understanding the effects of influencer marketing on consumer outcomes. However, there's a limited understanding of influencer marketing's impact on impulse buying. Signaling theory posits that information asymmetry between marketers and consumers can be reduced through credible signals. This study applies signaling theory to examine how influencers use signals of credibility to influence consumer behavior. The SOR model explains how external stimuli (influencer posts) affect emotional and cognitive states (organism) that result in specific behaviors (response, such as UBI). Previous research has explored source credibility (attractiveness, expertise, trustworthiness) and its influence on trust. Message credibility, relating to content quality and accuracy, and media credibility, related to the authenticity and genuineness of the platform, are also important. Trust plays a crucial role in reducing uncertainty and easing the buying process, impacting impulse buying. Product affection, positive emotions about a product, further mediates this relationship. Persuasion knowledge, the consumer’s understanding of marketing tactics, can influence susceptibility to influencer marketing.

This quantitative study used a structured questionnaire to collect data from 481 Pakistani social media users who follow influencers. The questionnaire measured influencer credibility (similarity, expertise, trustworthiness), message credibility (informational value, vicarious expressions), media credibility (interactivity, transparency), trust in branded posts, urge to buy impulsively (UBI), persuasion knowledge, and product affection. A five-point Likert scale was used for all variables. Partial Least Squares Structural Equation Modeling (PLS-SEM) was employed to test the hypotheses. The sample consisted mostly of 20–39-year-olds (96.7%), with a nearly even split between males (54.3%) and females (45.7%). The majority had a Bachelor's or Master's degree (71.2%). Reliability and validity tests were conducted. Cronbach's alpha values for all constructs exceeded 0.80, indicating acceptable reliability. Convergent validity was assessed using Average Variance Extracted (AVE), and discriminant validity using the Fornell-Larcker criterion and Heterotrait-Monotrait ratio of correlations (HTMT). PLS-SEM analysis was performed to examine the relationships between variables, including mediation and moderation analyses.

The findings support the proposed hypotheses. Influencer credibility, message credibility, and media credibility all significantly and positively impact trust in branded posts. Trust significantly and positively impacts UBI. Product affection mediates the relationship between trust and UBI, meaning that trust leads to product affection, which then increases the urge to buy impulsively. Persuasion knowledge moderates the relationship between influencer credibility and UBI—higher persuasion knowledge reduces the influence of influencer credibility on UBI. The model explains 40% of the variance in trust and 33% of the variance in UBI. Goodness-of-fit indices (X²/df = 1.616, GFI = 0.951, CFI = 0.961, SRMR = 0.060, RMSEA = 0.066) indicate a strong fit to the data. Effect sizes (f²) revealed that trust (0.703), message credibility (0.396), and product affection (0.219) had large or medium effects on UBI. Predictive relevance (Q²) values for UBI (0.444) and product affection (0.295) also suggest good model predictability.

This study demonstrates that the credibility of communication factors in influencer marketing significantly influences consumer trust and subsequent UBI. The findings support the integration of signaling theory and the SOR model to understand this phenomenon. The mediating role of product affection highlights the importance of creating positive emotional connections with the product through influencer marketing. The moderating role of persuasion knowledge suggests that consumers with high persuasion knowledge are less susceptible to influencer marketing. Marketers should prioritize credible influencers, high-quality content, and appropriate media channels to foster trust and enhance the effectiveness of their strategies. Addressing the influence of persuasion knowledge is vital for marketers aiming to leverage influencer marketing ethically.

This research provides valuable insights into the dynamics of influencer marketing and its impact on impulse buying. By integrating signaling theory and the SOR model, it reveals the crucial role of communication credibility in building trust and influencing UBI. Future research could explore other platforms beyond Facebook, investigate cultural differences, examine the role of advertising literacy, and adopt experimental designs for stronger causal inferences. Moreover, exploring the impact on actual purchasing behavior, rather than just UBI, and investigating the influence of other communication components would further advance this field. The ethical considerations surrounding persuasion knowledge and transparency should also remain a central focus for future studies.

This study has several limitations. First, it focused solely on Facebook, limiting the generalizability to other platforms. Second, the sample was limited to Pakistani social media users, potentially limiting cross-cultural generalizability. Third, the study relied on self-reported data, which may be subject to response bias. Fourth, the study focused on UBI rather than actual purchase behavior. Future research should address these limitations by including a broader range of platforms, diverse demographics, and alternative data collection methods. Employing experimental designs could establish stronger causality.