Fallout 4 players have discovered a way to get as many bottle caps - the in-game currency - as they want.
Here's how it works: buy all ammo of one type, for example .308, from a vendor (this seems to work with most vendors, but not all). Now, sell back one of the rounds.
Sell back the remaining rounds you just bought. One round glitches and stays with you for some reason. Keep selling this until you've rinsed the vendor of bottle caps.
You can take this glitch further and rinse the vendor of all its items. Buy back all of the vendor's rounds. Then, buy whatever you want and accept the trade.
Remember, vendors in Fallout 4 replenish their bottle caps every 24 hours. So once you've bled a vendor dry, sleep for a day, rinse and repeat. The video below explains how it's done.
Bethesda will likely patch this exploit out of the game sooner rather than later. Until then, go nuts!