On this page of our guide to GreedFall, you will find a walkthrough for An Aspiring Merchant, one of the side quests.
Where to start the quest?: New Serene, after talking to Constantine.
Talk to the merchant, and then go to the Coin Guard Barracks. Talk to the captain to get permission to trade, then, go to the specified location and talk to the Minister. You can use charisma to convince him and get permission to trade - hand it over to the merchant.
You will find that the merchant's goods have been stolen. Go back to the barracks. Speak with the captain and then talk to the person responsible for the prison (this person is on the floor below). You learn that the goods have disappeared. Go to the Coin Guard Tavern and participate in the arena fights. Choose the options in which you tell that you want to fight alongside the prisoner. The fight may be too difficult for you at an earlier stage of the game - you have to defeat that, e.g. a warrior and the two charging beasts.
When you win, go back to the merchant and tell him everything. You will get +2 to Islanders reputation. The merchant will also tell you to meet with Ullan, the leader of Vignamri. The leader is in Glendgnamvar. "The Shore of the Tall Bones"
Speak with the leader to complete the quest. You will also get 1,400 XP. If you accept the leader's offer, you will receive A Peculiar Alliance side mission.