Folks may ask you for something, but what they also want, or /should/ want, is the truth. Hell, even if they don't want the truth, they should be prepared for it.

And sometimes that truth - about you and from you - is legitimately that you cannot do the thing they want you to do, or that you simply do not want to do it.

I am a firm believer that being honest with people is more important than pleasing them.