To do this method, you must have a Barter skill of at least.... 2! I'm sure you can manage that, but the higher it is, the more profit per cycle.
Step 1: Go to a Weapon Dealer and initiate the sale.
Step 2: Purchase a WEAPON, I found the Laser Pistol worked nice.
Step 3: Sell it back to him.
You will see that when the item come into your possession, the CND went up. This is because the guy's a dumbass and thinks you make it look nice. It is now worth more in YOUR hands everytime, so if you make the sale again you make around +60 Pure Net Profit.
Once you have gotten everything possible (Keep an eye out, as some things will not work and you'll become poor...fast), you can then purchase all of your desired ammo. Then with this lil' salesman technique, you can re-obtain all of the money you just spent on ammo!
Hey Presto! You can run the derelict, un-glamorous, decadent, ruined, stale Wasteland out of bussiness.
*NOTE: Unluckt guys I tried it with the FAT MAN and the Alien Blaster... No such luck.
P.S. You then have to wait for the sale-person to have more money.
I currently have 51,615 to spend however I wish, too bad the best looking hoooker's a Ghoul!