The recent addition of Instagram feature, ad labels for sponsored posts, enables users to explicitly identify sponsored posts, increasing the level of transparency of posts (O’Brien, 2017). In sponsored posts in social media, followers are aware the marketing efforts that go on behind the user generated contents and message threads. Thus, the impact of postings on the followers’ behavioral response may vary depending on the levels of trust that followers have with the brand sponsored Instagram posts. In that regards, retailers implementing Instagram platform have faced creating more persuasive postings that can build the posting credibility and generate positive responses toward the brand. Grounded upon the Elaboration Likelihood Model (ELM) (Petty & Cacioppo, 1986), this study attempted to identify determinants of persuasive postings that build the message credibility of brand sponsored Instagram posts and positive responses toward the brand and to examine how the levels of trust followers have with the brand sponsored Instagram moderate the persuasion process when followers elaborate the postings. Data was collected via online survey and a total of 263 responses were determined to be usable in this study. Structural equation modeling was used to test the study hypotheses. The study results showed that post popularity and the argument quality of the post were determinants of the persuasive posting, increasing message credibility and yielding positive response towards the sponsored brand. Interestingly, post attractiveness was not a persuasive post characteristic. The results implied that post popularity and argument quality of post increased Instagram post credibility. These characteristics of posts have persuasive power to increase the post credibility, leading to a positive response toward the sponsored brand. Consumers’ levels of trust on the Instagram post sponsored brand moderated the persuasive process. The result supported that consumers with a low level of trust on the Instagram post sponsored brand carefully read a wide range of information and pay more attention to argument quality of posts, which consisted of the post content and other followers’ input regarding the product. Through the lens of Elaboration Likelihood Model, this study suggests that retailers should pay particular attention on the argument quality of a post and post popularity. The argument quality of a post is the influential factor determining persuasive and credible posts, further leveraging post credibility for consumers with a low level of trust on the sponsored post.

The purposes of this study were 1) to analyze the correlation between Word-of-Mouth(WOM) message sender credibility and WOM effect and 2) to analyze the differences of WOM message sender creadibility and WOM effect in off-line and on-line WOM communication. The messages were created as a form of scenario for this study. Respondents were asked to evaluate the message sender credibility and predict WOM behaviors after reading given scenario. The questionnaires were distributed to 200 customers and a total of 175 questionnaires were used for analysis(87.5%). The statistical analysis was conducted using SPSS Win(12.0) for descriptive analysis, paired t-test, factor analysis, correlation analysis. The positive off-line WOM message sender was considered as more credible(p<.001) than on-line WOM message sender. 'Message sender credibility' is correlated with 'attitude formation' in both channels, but 'reliable' factor of 'credibility' variable is not significantly correlated with 'attitude change'.