I've been modding for a few years now, only doing basic dialogue and world building. I've had an idea for a quest mod for sometime now, so I've taken it upon myself, lately, to learn all aspects of the CS. I've been doing pretty well, so far. Writing basic scripts, understanding more complex one's. But the advanced dialogue is what I'm having most trouble with. I'm trying to make it so you can't barter with an NPC until you are a certain rank of a certain faction. I know it's done in the vanilla game, but can't seem to find an instance of it. Is it done through scripting? I'm just not sure. Any help would be much appreciated.

http://postimg.org/image/phasci9q1/

Wow! That simple, huh? Thanks! I've been stumped for hours on this one. I feels kinda dumb now.