Well, I have no idea how to make it about NPCs, I'd probably be looking at The Operator's Reputation move.
But I wanted to chime in and say that if I were writing this, it wouldn't give your opponent -2 on your Read a Person rolls. It would let you spend the hold on their behalf instead, as long as you told them something they didn't already know. Thus ensuring that the Secretmonger still has to answer questions, and come up with weird allusions to other secrets, but letting them avoid the issue they actually want to keep hidden.
I'm guessing this entirely from the name, but I bet that if you're playing a Secretmonger then really you want people to be suspicious of you, to be trying to read you, but never quite to be getting what they want.