This quest is mostly identical with the exception of the reward and who hands it out; Helena for the Knights and Marvel for The Righteous.
There are two choices here. You can attack Rafeallius to get the key you will need to get the diamond from his body, which will mean killing the other three vampires, or you can do the jobs he wants.
Once you have the nuggets, return and speak to Rafeallius again. In return, he gives you the key needed to get into his locked workshop in the basement, and tells you how to get into the hidden room where the Gorvette Diamond is stored.
On the desk in the workshop is a statue of Kynareth. Activating this opens a secret door in the corridor where there is a chest containing the diamond.
Return to Helena or Marvel with the Gorvette Diamond, however you obtained it. Helena gives you 125 Gold; Marvel 100.
For both Varo's Knights and The Righteous you are going to be taking the place of a person that the other group believes they are dealing with, and thus wrecking a transaction.
"This may not be so easy. I need to locate an amulet, presumably somewhere in Shanar's house. Then try and pass myself off as a rebel contact. Then I will need to return the amulet to Shanar's house. I hope my burgling talents are up to this. Breaking into a house once undiscovered is bad enough but twice...!"
"This job isn't off to a good start. I completely forgot to get the amulet. Needless to say, Golent figured out I wasn't the contact immediately. On the bright side, I don't have to worry about returning the amulet."
Golent is suspicious of you, even if you are wearing the amulet, and will ask you several questions.
"Who is the leader of the Righteous?" - The Saint.
"At least you are not clueless. You know that last time I was in Windfall there was a Righteous member in the club. All he would ever talk about was women. In fact, he was in Windfall because he had gotten himself in a spot of trouble. It turns out he was caught messing around with a general's daughter. Now what was his name?" - Fiorde Club-Fist.
"If nothing else, you have obviously heard some if his tales. Ole Fiorde is a chatterbox when gets to drinking, isn't he? What was the name of the Tavern he likes to hangout in?" - The Thirsty Peasant
Should you answer them all correctly, he will then be happy. Otherwise, you will have to kill him and the others.
"I blew my cover. Not the best solution but I don't think Helena really cared that much. I'd better return the amulet."
Take the amulet back to Shanar's and put in back in the box, then return to see Helena. She will pay you 150 Gold and, assuming you didn't wind up killing Golent, give you a Base Necklace of Mercantile.
"Well now this is interesting. The rebels have learned that a man named Menard is about to con the Knights out of their heirlooms. Now I need to kill Menard, so I can con the Knights out of their heirlooms. There is a perverse kind of justice in that. Sounds as if I'm going on a killing spree. Still I'd better try to convince Marcea that I am genuine first. I am not keen on killing innocents. Even those who are misguided"
"He he. They'll return to an empty welcome. Still, at least they're alive. Better get back to Marvel with the good news."
Return to Marvel who takes the heirlooms from you and gives you 120 Gold. If you had to kill Mercea, Marvel only gives you 60 Gold. If you failed to kill or dupe Mercea, you get nothing.
Your next quest is to stop attacks on road traffic in A Raid.