If it comes from a trusted source, we're more likely to believe it. If it's coming from someone who doesn't have much credibility, we're more likely to be skeptical. Think of it in terms of high school. Perhaps the gossip is as simple as who's dating whom. Well, not really.
Human relationships are complex.
We're constantly evaluating and re-evaluating our sources, relying on visual cues, factoring in history, determining motives. That's harder to do online. For example, the idea of travel bulletin boards sounds great at first. It's hard to get any sort of hard, real information from a lot of them. If it's just one comment from one person, you don't have any consistent basis to judge what their style is like.