I recently need to response to some lengthy complains with close to 10 points there.

At first, I was frustrated and just forwarded it to the targeted party. It's their job anyway. Then, I realize it's a collaboration. If I don't help them to drill down those complains, it affects me as a so-called middle-man also.

So I took a deep breath and carefully asked these questions

- is this what you meant ?

- this is their explanation, based on my understanding, it seems fine, how 'bout you ?

- they also provide some data. Let's see, you got some data erh, that might show something different ?

And with those, the questions dramatically went down to less than 3

It's still a long way until we can address all but at least, to remind me (as I haven't done this quite effectively though):

- the longer the complain is, the more we should take them with a grain of salt

- apply some filter, ask for data, it's effective

- be objective. try to think 'bout the claim, not the people who claim it. if you know that what they complain about is sux, it doesnt mean their complains are always valid though