Karmic Justice

Karmic Justice  is one of the undocumented quests in  The Witcher 3: Wild Hunt, and can be obtained by walking in the Novigrad suburbs near the river, between the Tretogor gate and the Southern gate.

Walkthrough
You will find three elves trying to kill a merchant. If you talk with them they will tell you the man sold poisoned fisstech to their young ones, and they suffered a painful death because of it, and they have come for revenge.

You can ask about searching the man to check if he has fisstech, but the elves will answer they couldn't find anything because they think he sold everything. The man will deny the accusations and pledge for help arguing the elves are just trying to rob his gold and blame him for their decadent society.

If you decide to help him because there isn't enough evidence to kill him, you will fight the three elves. and the merchant will reward you. If you decide to let the elves carry the punishment, you receive nothing.

At the end of the quest it is not clear if the merchant is innocent or not.

Note

 * If you trigger the quest (ex: Hear their talking). To wait too long before joining them or just walking away, the elves will kill him and you won't be able to help him or interact with elves.
 * If you don't trigger the quest (ex: Stand a far away watch them. In this case, the NPC won't acting until you close enough). This quest will mark on the map to remind you to come back later.
 * One of the elves might try to kill the merchant while you are fighting with the others.
 * From a profit-oriented perspective, it is better to help the merchant. Because you will earn some crowns, experience points and loots of the elves dead bodies. While letting the man die gives you nothing.