Overview
Suspicious Shakedown is an unmarked secondary quest in The Witcher 3: Wild Hunt, available after Pyres of Novigrad. It takes place in an alley behind a house just north of the Rosemary and Thyme in Novigrad, almost directly north of the Gate of the Hierarch signpost.
What happens
Behind a door in the alley, bandits are threatening a merchant for money. They tell Geralt to move along. He can leave, in which case they take the money and let the merchant go. Or he can protect the merchant by threatening the bandits, which leads to a fight, or by using Axii to send them off.
Why it matters
The merchant runs a shop in Silverton. If Geralt walked away, the merchant refuses to trade with him from then on. If Geralt helped, he is happy to see the witcher and even mentions a discount, although prices do not actually change. This quest is also part of what triggers A Feast for Crows.