Let's start from the start.
I think that there are two types of hard riddles. One: whose answer is very hard to guess. These riddles are interesting (in my opinion) and always leaves us something to learn. Two (broad): there are too many possible answers for this kind of riddle and the only hard part is choosing which answer matches better. I think it's annoying. And usually people answer multiple answers in a single answer. (You know what I am trying to say!)
The first kind is perfectly great but here I am concerned about the second. Something that happens usually on these kinds of riddles is that the whole webpage is covered with all the possible answers and sometimes even after 10 posted answer, the OP doesn't get his intended answer. Usually OP posts a hint after 3 or 4 answers to narrow down the puzzle. But is it what hints are for ? To narrow down the puzzles? Hints are to show the direction when there is no where to go, just like a catalyst.
Hints should be used when there is nothing that our peers can think. In my opinion it should not be posted when there are too many possible answers because in this case the riddle itself is too broad.
Should we accept the riddle with the hint? I mean, it's upto the answerer if he wants to read the hint(s) or not because well, riddle should be solvable even without the hint.
Should we flag the riddle as too broad without looking at what the hints say?
This thing is usually found in the riddles and that's why i typed 'riddle' this whole time otherwise it is equally valid for other kind of puzzles.