Also, while asking people that sort of question, ask yourself whether improving the situation is within your reach, whatever is the cause? If you think you could -- do you think people you are interviewing, also believe you can?

I wouldn't tell anything to a person who has no power or no incentive to improve things, and sadly, this covers 100% of people one usually has exit interviews with. So I always declined them, politely.

You wouldn't believe how much respect and good contacts this attitude earned me over the years.