A service like this might be useful for people who run communities to keep unwanted content away.
1. How much would you be willing to pay monthly? 2. What is the top feature you want out of this?
Allowing users to make reports is NOT the hard part -- I can throw together an HTML form and a DB for reports in about 1 day.
The HARD part is finding a way to make these reports useful and actionable. To make sure that they ADD value to your community-building rather than subtracting it.
The exact solution depends on the community. And it must address issues like spam, false-reports, reporting for disagreement instead of concerns, reports that are ignored, and the fact that users don't actually agree on what standards of content ought to be acceptable.
IF someone had a reporting system that addressed at least some of these issues, then it would be extremely valuable. But the top companies in the world addressing these issues don't seem to have figured out an ideal solution yet; I doubt you have one.
1. Spam: Humanity verification + A Negative Points System*.
2. False Reports: Negative Points System.
3. Reporting Disagreements: Negative Points System.
4. Ignored Reports: Regular Reminders. Prioritizing content that multiple people reported.
5. Acceptable Content: The community owners decide standards. Not this system. The owners can merely use this as a tool for reports to come in.
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Negative Points System: Everyone starts with a X number of points. Each report decreases X. If a report is constructive, they get back decreased points, plus earn some. If the report is well intended, but doesn't justify a report, they get back points, but earns none. If the report is malicious, they lose their points, and some more. The pluses and minuses can indicate a user's behavior, and the owners can remove that user's right to report.