Treat each post on its own merit; if you see a pattern of behavior go ahead and send up a custom flag.
Posts should be voted/commented upon regardless of author. We're all human, of course, but to the extent that we're aware that we may harbor a bias against an author (borne of experience), we should double-check ourselves that we're voting the post, not the user.
That said, there are times that a user is doing... ~things~, none of which seem, individually, to merit action but which, when taken as a whole, bother you. In that case go ahead and raise a flag for moderator attention, please. One of our charges is to keep an eye out for "consistent, low-quality contributions over time."
We have some tools to help with that, we raise flags ourselves just to keep our eye on someone, but it's a tough job, it's a subjective job, and it requires sustained effort. Luckily, that's exactly the sort of problem that an educated and well-intentioned crowd can help a lot with.
The "in need of moderator intervention (be specific)" flag reason is great for this: raise a flag on any post by the author and explain the pattern you're seeing. You probably won't see any response from us*, but please know that we appreciate the help!
* - If we end up taking no action it's strange and hard to go back and find the initial flagger to explain; if we do take mod action it's not really appropriate to do so.