This is going to be the best post of my life!!!
I think I can't get any better than that.
1) position character on a market place;
2) select some items in inventory;
3) set prices;
4) set offline-mode to "vendor";
5) go offline (character becomes an NPC vendor);
Edit: I had to add this line:
inb4 crunch selling his cigars, weed and microphones