Long term the goal is to have an open reputation score for every fact checker. I'm currently experimenting with different implementations of this, and seeing good promise.
For example, I believe HN has a vote-ring detector, but I think there's also a decent amount of manual intervention from the mods. Amazon's reputation system is under constant attack through a variety of means (paying teams of people for fake reviews, going to the length of having real transactions on Amazon between fake-reviewer and the seller buying the review).