Mentioned in this question: What are ammo boxes for?
I honestly have never heard of this glitch...though I didn't spend much time going through FAQs or anything while I played through Fallout 3.
I debate trying it out when I pickup New Vegas...and am curious as to how one would do it.
It's a glitch which allows you to -- under certain circumstances -- purchase weapons or armor from a shopkeeper, then sell them back for more than you paid for them, and to continuously loop that process, thereby giving you anything you want from the shop, as well as all the shopkeeper's caps, essentially for free.
This YouTube video demonstrates it on PC, and I've used it successfully in both Fallout 3 and Fallout New Vegas (already!). By the end of my last Fallout 3 run, I had over six figures in caps. Also, for a guy with less than an hour into New Vegas, I think I'm doing OK financially -- almost 800 caps.
The trick to it is having in your inventory a weapon or piece of clothing/armor which the shopkeeper sells, preferably at a lower repair value. Sell it to him, and commit the transaction. Buy it back and commit. Lather, rinse, repeat. It may take two or three repeats before you start buying it at its original value but selling it as 100% repaired.
If you're on a non-updated version of Fallout: New Vegas, you can buy casino chips and sell them back without them taking them from your inventory.
I have made 500,000,000 caps this way.
I use a broken down weapon ( 0% ) like a 9 mm pistol or a varmint rifle early on the game...get another same item before you trade with merchant. Save before doing this glitch as NV always freeze randomly. Now if say you have both 9 mm pistol with one having ----- value... Sell the other that has a value 1st then followed by the zero value item then buy it back picking the zero value pistol 1st as soon as you press on the accept button the other item turns into another zero value so you can get these items back without a cost to you... Repeat it over and over until you clean the merchant dry.... You can even buy ammo and stimpaks then get your money back. The problem is getting an item thats totally broken down. What i did during the gunfight in goodspring is that i used my VATS on the powder gang weapons to break it down to zero. I pick up this item then match with another to start my merchant glitch.
