Reputation would have to be a factor then, to limit the use of bots in this fashion .. I suggested 50+, or perhaps even more! There is no reason that people who have not invested any time in the platform be given the right to flag others who have.
Bots must be pretty easy to identify, given access to account / login information (location) and blockchain activity .. perhaps one downvote per post, per IP within a 24 hour period. Certainly some 7-proxy wizards can take on that challenge, but .. wow, what a waste of a life, just to sneak some literally-lousy bots in to do some entirely destructive flagging, that gains the bot-master nothing? Once identified, these bots should be completely destroyed for breach of terms, and whatever STEEMPower they have collected would go into a pool for later distribution to the entire LEGIT userbase! :)