Fallout 4 isn’t particularly an easy game, especially when it comes to managing your equipment and gaining weapons that really deal good damage to all the dangerous inhabitants of the wasteland. Luckily, there’s already an optional exploit to maximise your income.
The glitch can be done at any merchant that sells ammo. First, buy all their ammo of one type. After that, sell back one ammo at a time. Repeat this six times and then sell back all the remaining ammo. Most of the time, you will still have some ammo that can be sold infinitely – at least until the merchant runs out of cash. However, you can repeat this at any other merchant. Just make sure to save your game before this glitch, as this is certainly not intended by Bethesda. Here’s a short video that confirms and shows this exploit.