One member warned another not to do business with a third member.
She had heard too many bad things about the third member. First she posted the warning privately. Then she posted the warning publicly.
All hell broke lose.
In private, these allegations aren't a problem. In fact, they're beneficial to enforcing desired community norms.
However, if the allegation is posted in public, things spiral out of control. The subject of the allegation is forced to respond to defend his status. Bob's friends must also defend him or risk injury to their own status.
These attacks soon get personal and move into dangerous ground (morally and legally).
There are three solutions here. Each solution has its downside.
The first is to ban public allegations against individual members. But wouldn't it help a community to know if a member had a track record of causing problems for members?
The second is to require tangible proof to support the allegation. This sounds logical, but what is considered proof? Is support from a member's friend proof? What is the bar to reliable evidence? Does this place you in dubious legal territory? Do you allow statements from the member? Do you allow appeals? Judges? Juries?
The third is to tell members to come to you with such accusations. You can look at the evidence, get both sides of the story, and make a quick judgement call. This works, except it's likely to foster resentment against you.
When dealing with a public statement that is critical of another member, be aware of the social dynamics in play.