A niche moderator's primary mission is to ensure that the content posted to the niche matches the niche's subject matter. If it does not, no matter how good the content is, it should be removed/not accepted in that niche. We want to make sure that if someone follows a niche that they are always seeing content that reflects the specific subject.
Quality should not factor into a moderator's decision, because quality will be determined by the community at large.
Moderators should screen and report any potential ToS and AUP violations.