Dragon Age 2 Quest Reference: Act 1 - Secondary Quests - Finders Keepers
Requirements: Fools Rush In
Go talk to Isabela in the Hanged Man for the Isabela's Contact quest, she'll point you to Martin in the back who will start the quest. He'll explain the quest and send you off to the Docks (day). After a conversation with Liam, you'll be foisted off on Aden. At this point you'll have three choices: you can bribe him, threaten him, or refuse to pay and steal it. Threatening him will not always work, your chances are higher with Varric in your party. Bribing him will cost you 2 sovereigns. You can also return to the area at night, kill the guard dogs and steal the redirect from the table. Note: Even if you don't see the option to go at night, you have it. Just return to the same place and steal the documents. Be sure to find the entrance to the Disused Passage in the office, you'll find the Remains of the Outlaw "Half-Braid" Silsam there, which is part of a find and deliver quest.
After getting the Dockside Redirect, you can either go to the Woodrow Warehouse during the day or night. The day time trip will see more fighting outside the warehouse with the guards. There's only one guard at night. Again, your quest marker may not reflect that you can go at night, ignore it and go anyway. Once you get into the warehouse you'll have to fight the same number of raiders day or night. Be sure to look the room in the south of the warehouse for a chance at loot and the chest in the NW room. Be careful with the traps in the entrance area of the warehouse.
Go back and see Martin during the day when you're finished. You can refuse to go along with him, give him the cargo information for free or offer it for payment. The best option is to offer him the information for free. If you do this, he'll become available as a poison vendor.