Kind of repetitive from last post. But don't lie.
Just say, you can't tell any more than the NPC is telling you.
You don't have to. If the check is successful tell them the NPC is hiding something or if really high, tell them something deeper as you see fit.
Heck you could use
@iserith 's preference and allow insight to instead (it in addition) SUS out ideals bonds and flaws.
I see no reason to have the player pretend they don't know something they think they do - that just leads to absurd and worse, uncomfortable, game play