I have talked to a Witness about this the take away is always“whatever the blockchain allows.” There is no way to determine for them what is “valid” flag or not because everything is considered valid. One can simply ague they disagree with the reward of that post/comment and it’s vailed for a flag among anything else.

I ran into this problem when trying to debate an argument and realized I was asking them the impossible. The only thing there is, is how certain community members feel about using the flagging system, and your own personal ethics/believes on what should be flagged or not. They would first need to come up with a hard outline of what is considered flag abuse as there is not one.