I always thought of it the other way around. NPCs can make outrageous lies and either they are caught out by inconsistencies in their story or the PC makes an appropriate roll to detect the lie. In BRP that'd be an insight skill roll, or some kind of Perception roll.
Originally Posted by soltakss
I don't really think an NPC needs to make a roll, in fact I would go as far as to say that an NPC shouldn't make a roll to lie. It's a give away to the players... NPC says "I am the king of Atlantis" GM rolls dice and says "he seems to be telling the truth". When have you ever had to make a roll to tell the truth? My players would become immediately suspicious... However, NPC says "I am the king of Atlantis" Player says "Really!? Is that right..." GM offers the player an Insight/Psychology/Perception/Human Lore roll to 'read' the NPC.
Mr Jealousy has returned to reality!