Only posts can farm reputation, the number of authors doesn't matter. To farm reputation from posts, you would need an automated post creation algorithm that passes the Turing test (or an algorithm that creates useful content for the community, which would be legitimate). Ultimately, authors that already have reputation decide which posts receive reputation. I believe that would be difficult for a small number of malicious authors to take control of the community trying to be smart, but I don't have any strong evidence though.