Is it ok to lie to players rolling a insight? [closed]

I’ve just started DMing.

I have a question about the Insight mechanic. I’ve formulated this problem using D&D but the system is otherwise irrelevant, I’m just asking about idea.

How does insight work? Is it about expectations of players or actual situation (bluff or not)? Is it ok to lie in response to a low result as long as it’s what the player expects?

Let me present an example. Let’s say I have a paladin in my game who is evil (but the players don’t know that). He asks the players to kill some evil people, his servants. The paladin’s motives are to kill the servants because they were disobedient as well as kill players because they are threat to him. This request is probably suicidal because the players probably can’t accomplish the task. The paladin knows that.

One of these servants is cruel, bloodthirsty and totally opposite to the paladin’s behavior. After a fight with this servant, the players talk to him. He says that the paladin is his leader.

That seems absurd to the players, so they roll an insight check and get a 5, which is far below the DC.

What to do?

  • Lie to them that this guy is bluffing? He’s not but it fits in expectations of players.

  • Don’t roll at all in the first place because no deception has occurred.