Goblin Queen (She/Her/Hers)
I don’t need to know how well he performs. I’ll describe the action (the lie), and if the player suspects it’s a lie, they can describe an action to try and determine if it is or not. At that point (assuming the player’s approach could succeed or fail), I’ll call for them to make an ability check, probably Wisdom (Insight) contested by Charisma (Deception). If the player succeeds, I’ll give them whatever information they were saying they were trying to learn with their action (as established by the goal they stated). On a failure I won’t. Either way, the player is free to decide how their character thinks and feels about that information (or lack of information) and if and how they act on it.Let's try it another way then, an NPC tries to deceive a PC, and as the DM you don't know how well he will perform in his deception, so the result is clearly uncertain.