This makes sense but I think still has a small problem. Someone with good real life people skills is going to be better able to put together a cogent argument, or understand the social dynamics and where to apply pressure.

I don't really know how to solve this. It quickly becomes a "players making these decisions is the whole game" thing.

But I do think that if you have someone who's trying to be a social face without the real life skills, it is okay for the GM to give more hints. Remind players that the knight respects honor and honesty, that the thief is scared and just wants to eat, and so on. Hopefully from there even a shaky player can figure out being honest with the knight is a better move than deception.