The baseline model is reddit. You start at 0, and if you get negative you're timegated from replying. HN has a karma system as well. You need 500 karma to downvote (or something to that effect).

Honestly, I think something like a StackExchange lite reputation system could work well here. But as more for a credibility system than an authority one. Someone with a good reputation (by the users and the site itself) is probably making more credible reports than a newer person or a troll.