Role playing games are about playing a role and social interaction is where players can really get into their characters. The Game Leaders and players should adopt their roles and act out the conversation. Only when the Game Leader is happy that the players have been convincing will the characters get what they want from the NPC.
This approach favours players who like story-telling and are good communicators in real life. It also helps when the Game Leader has a clear plot to the adventure. They can give the players as much or as little as the plot demands without worrying that a lucky or unlucky dice roll will hinder the progress of the adventure.
The flip side is that players who are less comfortable with this style of play are disadvantaged. Role-playing games don't expect their players to be as good at fighting as their characters so why can't a player have a character who is better at communicating than themselves?