What you're talking about is a great example of good-faith communication. Unfortunately, it relies on both parties dealing in good faith, and I've had too much experience with people who won't do that -- they won't give an honest assessment of what happens if their request isn't met. I wish I knew how to handle that.
In this case you should trust but verify: ask the person to detail his sources (he is making the request on behalf of someone after all) and approach them directly to get a better picture of the situation.
If his sources are outside of the company or also not truthful then I'd also be at a loss :)
