This is glitch is only available AFTER you beat and finish the Old World Blues Add-On for Fallout New Vegas.
Steps:
1. After you leave Big MT, Choose the wait option and wait 3 times 24 hrs each(or 4 times fo safety).
2. Use the Gun given to you to transport back and go to the Sink(your butler).
3. Go to buy items.(make sure he has 4 proton axe's in the weapon catergory that u can buy from him and doesnt matter if you have any on yours.)
4. Make sure his item selection n yours is on weapons.
5. Buy the cheapest axe from him and after the price should have increased for selling price to him. (as in the video,every now and then itll change but go back to you making more.)
6. After you get on the caps out of him, leave and go back to the mojave.
7. Repeat all steps and your filthy rich,it can be done over and over.
Figured id share what I found since i havn't seen it anywhere else.
EDIT: been known about the inf cap glitch for sometime but ever since i put the 1.07 patch on i havnt been able to do it with any vendor until i got to sink n im on the ps3 so i figured it was the same for everyone else playing on ps3 so i posted it thinking it would help.