Surprised no one has noticed yet, but doing this depletes any stock of the ammo type you use for the exploit in your own inventory.
E.g. if you use .308 ammo to do the exploit, when you are selling the glitchy single bullet to get all their caps, I noticed that when I completed the trade, all my .308 ammo was missing. All of it.
No matter what I did, I had to sacrifice one ammo type to get it to work. So it's not that great really. Might as well use console commands, cos ammo is pretty important.
Edit: I just realised I didn't try buying the ammo I sold back in the same trade, which, if my logic is correct on how this works, should yield infinite ammo AND caps. DAMMIT I now have to wait until I finish work to try it.