It could be "if your fact check gets flagged a lot we'll review it and punish your reputation if it's inaccurate."
Not ideal to leave Google in control of Truth (and they might not want the burden), so it'd be interesting to offload that responsibility to Wikipedia, which seems to have a pretty good system for coming to a consensus.
Google mentions this in the docs, but if it's page ranking, that can be gamed, and if it's "pay us to be a fact checker", well...