Hiya!
Players can request that...but I do the rolling, behind the screen, then tell them something. I base the DC on how good the NPC is at Deception. Typically I'll choose the Deception DC based on the details of the interrogation/question. I mean, if the PC's have an NPC dead to rights with his hand holding a cookie and crumbs all over his shirt, "Did you eat the cookies?" will probably have a pretty low DC. Like, maybe 4 or 5. But if the NPC is completely confident and the PC's have virtually nothing to go on, the DC is probably in the high-teens to low 20's (18 to 22 or so), or maybe even higher.
Then I roll. If the Player beat the DC, I'll give him a REALLY strong hint, pretty much obvious: "You're pretty sure he's hiding something, and he gets visibly nervous to you when you mention the cookies going missing". But I NEVER say "Yeah, he's lieing". If the Player failed the DC, I'll either just say "Seems to be telling the truth", but if the Player failed miserably (by 10 points or more), I may give a slight hint the other way: "He seems to be telling the truth, but he did glance over at your half-orc hireling with a bit of a nervous look...". Or, of course, the other way around (so if the NPC is innocent, the PC might be told "He's definitely hiding something, and glances at your half-orc hireling..."...but what he's hiding may not be what the PC's are on about).
In short, Yes, but I roll in secret for the Player and I give a hint or strong hint. Ultimately it's up to the Player to decide what to do with the information. Making an Insight roll is not the same as casting Detect Lie.
^_^
Paul L. Ming