I think that lies are important in games, specially in RPG. When you like evil sides you could lie for several reason, making conflicts, make people suffer, send them to a trap, fool them and so on. So it's a part oh your character that exist in you every day life, not just in quest time. But it must be a two side effects as if the npc realize you'v tried to fool him your level of respect can go low depending of who you try to fool. I think it could be a "simple" effect as if you lie to someone but in an other conversation you say things in an other way thoses npc could meet each other and discover your lies. People could also see that you lie and could react differently, nicely and say don't fool me, attack you, spread your lies... Well anyway my poor examples, lies are interesting in game because they give some oportunities to set out of the main line. About the rolling issue i think that liying is not natural and not every one have the same reaction. So it's not as simple as you can lie for everyone and they all trust you.