Invest in stores. -- Think oblivion. Idea would be if you have barter of 70+ you can invest in a store. This would give them more cash to buy your goods. If possible, perhaps increase the amount of ammo and etc they have for sale.
Bank your cash! Gain a flat percentage rate on your stored cash. It'd be a neat place for others to stage bad things to happen to your cash. (market crash? Bank robbers?)
Hire mercs. -- mercs, loyal to you patrol trading routes. Caravans can pay a "tax" for protection. Chance at mercs dying randomly every day or if your around and see them die you will have to hire more, Could extend this to protecting towns and etc. Perhaps lower their mortality rate by buying them various weapon/armor packages. (Think text dialog, 10k spawns a single merc with combat armor, etc etc.)