You must have an unpatched version of the game to do this. Go to anyone that deals weapons. You must have 2 of the same weapon, and some caps. Sell both of the weapons and buy back the one with the lowest conditioning. Sell and buy again until you notice that one has fully been repaired. When you buy it, it will keep coming up as the original weapon, but when you sell it, it will be in perfect condition.... so you'll be getting constant caps. Buy everything the person has on them, then repeat the process to get your money back!