Credibility evaluation has become a daily task in the current world of online information that varies in quality. The way this task is performed has been a topic of research for some time now. In this study, we aim to extend this research by proposing an integrated layer model of trust. According to this model, trust in information is influenced by trust in its source. Moreover, source trust is influenced by trust in the medium, which in turn is influenced by a more general propensity to trust. We provide an initial validation of the proposed model by means of an online quasi-experiment (n = 152) in which participants rated the credibility of Wikipedia articles. Additionally, the results suggest that the participants were more likely to have too little trust in Wikipedia than too much trust.