When seeking information, Internet users often find multiple communicators co-presenting and expressing their opinions. This study examined how people judge message senders’ credibility in a multi-source environment based on system-generated cues, the consensus among multiple sources, and the effect of receiver’s familiarity with the online platform. Moreover, this research examined the mediating role of source credibility in attitude change in an online consumer-review community. Results indicated that users familiar with a platform were more likely to use system-generated cues for their judgment of credibility along with consensus heuristics, and the combination of heuristics influenced attitude through credibility. However, unfamiliar users relied on consensus heuristics but not system-generated cues. These findings and their theoretical implications are discussed.