Use Social Combat

Review the Social Combat rules and use them. A lot of games don't have a good system, or any system at all, for this sort of thing, so you might need to consciously go looking for times to use it to begin with. Pretty much any time a PC wants an NPC to do something that they don't want to do, it's time to roll those dice. Even if the NPCs yield 9 times out of 10 when they're beaten, it's still worth it.