I think any complaint is to be taken seriously, even the *rs*h*l*s

If a complainant is very agressive then try to remove him or her to a controlled environment.

I recently faced a hoard at a festival who wanted to break in to the venue as they were unhappy with the ticketing system. I could not practice what I have said above but they got their way the next concert because I listened and spoke to management who listened and changed to rules accordingly.

It really was very agresive and violent verbally, and escalating if not careful to physical. Beer and hot weather make it worse.

We must just all do our best. Removal to a controlled environment where they can vent their spleen is often best, it is amazing how often they calm down when there is no audience for them.

Just a thought.

Andy