Fallout 4 exploits

Infinite Caps
When trading with a merchant the player buys a large quantity of one type of ammo (ex .308, .45, etc). The players does not complete the trade but instead goes to the to-be purchased ammo in their inventory and gives back one. The player then gives back the rest. Now the player has a single unit of that "shadow" ammo left in their inventory that they can sell back to the trader. After repeatedly selling back that "shadow" ammo for dozens of time, the player can then buy back all those "shadow" ammo sold to trader and in effect double the "shadow" caps you earned. This buy back action makes the whole rip-off process much quicker. The caps the trader owes you can then be traded for the rest of the NPC's inventory.

This can also work to your advantage when buying other goods from a vendor. after completing the first steps, instead of taking all of the vendors caps, the player can select all of the vendor's inventory and then pay the difference with the bullets in the glitch. In this case, it is better to use ammo with a higher value so the purchase process goes quicker.

Note
After selling some ammo back to the trader (about 100) go over to the traders inventory and attempt to buy all of the ammo back and it will keep increasing the caps much faster than selling a few bullets at a time

Works better if they have over 200 of that type of ammo.

Ammo is sold back to the trader for the value of ammo the trader is selling it for.

Slowly, over time, if the player continues to trade back the ammo, the number of caps being traded will moved to the left of the screen until it's gone.

If the glitch doesn't work for a trader, you can try trading ammo with the trader and try again or use fast travel then try the same trader. In some case this will make the glitch work again.

The type of "shadow" ammo used will be completely traded to the trader thus leaving the player none in inventory. You may deposit the ammo in a nearby container to preserve the ammo you need for guns before trading.

Confirmed to work

 * Some settlement store workers
 * Trashcan Carla
 * Arturo Rodriguez
 * Doctor Sun
 * Percy
 * Moe Cronin
 * Proctor Teagan
 * Becky Fallon
 * Solomon
 * Cricket
 * Polly
 * Synth
 * Trudy
 * Lucas Miller

Non-player character-specific exploits

 * Dogmeat (Fallout 4) is able to fetch the Cryolator without the required lockpicking level. Video example can be seen below