While playing through the Great Departure story mission in GreedFall, you will meet Sahin, the Ambassador for the Bridge Alliance. He asks you to investigate an Alchemist who claims to be selling a potion that can cure the Malichor illness. Agree to investigate, then head across town to the marked location.
GreedFall – The Charlatan Side Quest Guide
Here you will find the Alchemist at his cart, selling the potion to various people gathered there. Talk to him and exhaust all the conversation options. After, you will need to investigate. Head to the right, then go in the metal gate that you will be able to see if you turn left. Pick up the two items there, one will be a letter, and the other will be a potion. The plan is to make the Charlatan drink his concoction. You will get attacked by some thugs, but they will go down quickly.
Go back to the man and make him drink his potion, exhaust any dialogue options, and then follow him to the tavern he is staying at. Head upstairs to his room, and then you will have two options when you confront him.
Arrest him – if you wish, you can arrest the man. This option gives you reputation with the Bridge Alliance.
Help him escape the city – if you take pity on the man, and his attempts to find a real cure for the Malichor illness, you can decide to help him get out of the city. There are a couple of options on how to do this. First, you need to find a way to deal with the mob outside. If you have any points in Intuition, you can trick them into leaving. If not, you can give them six health potions. You can purchase them from any merchant. You can also fight the mob, but you want to avoid fighting them. Conflict like that is going to cause you to lose reputation with the Congregation of Merchants.
Whichever option you choose, when you finish head back to Sahin. You can choose to either lie to him or ask him why he lied to you. If you lie, you will lose no reputation points. Confronting him about his dishonesty causes you to lose some reputation with the Bridge Alliance.