To answer your question, I think someone shouldn't be able to get away with many "bad ratings". I don't think this should be a percentage, but rather a raw number, and that number should be very low. I would also view a "bad rating" that is being defended but may not necessarily agree with differently than a "bad rating" in which is not being defended. IMO the later should be viewed much more harshly, and should not be tolerated.
This is so absurdly specific, probably a projection based on something you've done.
A bad rating/flag is bad regardless if it's defended by the person who posted it, "supporters", sockpuppets, what have you. A good rating/flag is good regardless of who may try to discredit it.