Economics of Violence

 refers to an unmarked quest in Fallout 3.

Pronto in Paradise Falls complains about having no good items to sell as all he gets from the other slavers is leftover junk. If you offer to help him out he will ask you to bring him 20 Chinese Assault Rifles.

Rewards
Pronto's shop will have a better inventory and he will also get a bit more cash (around 400 instead of around 150).

You will also receive a "business partner" discount of 20%.

Glitches
Once you give him 20 rifles, if you talk to him about his inventory again and agree to get rifles for him, his inventory will revert to the crappy version. So don't talk to him about his inventory once you have given him the rifles.