We could also do network analysis on the graph of people reporting other people. If there are any strange, unnatural patterns, they could be ignored. But if Jonny has been reported by 10 people in the last month, and those 10 are unrelated to each other, that would be compelling evidence Jonny is not behaving well. The system can still be gamed if a group of people are organized online to report targets (like 4chan does DDOS attacks). Fortunately, in order to report someone one would need to disclose his identity. On 4chan there is radical anonymity, by contrast.