The Fishing Job

It is a radiant quest given by Delvin Mallory in the Ragged Flagon as extra work for the Thieves Guild. Fishing jobs consist of using the Pickpocket skill to steal a valuable, unique item from a random character. Fishing jobs can be declined at any time by talking to Delvin Mallory again. There is no penalty for declining or rejecting these jobs.

Doing enough additional jobs such as the fishing job in a hold unlocks the city influence quest in that hold.

Trivia

 * When Delvin ask that a gem, or piece of jewelry be pickpocketed, it can be replaced in order to keep the stolen one. Have an identical item in the inventory (it does not matter if tagged as stolen) when talking to Delvin to finish the mission. He will take the un-named "x" item leaving the named one. These can be of some use when enchanting rings or necklaces to avoid having to name them so they can be easily identified in the inventory.
 * Heimskr may be assigned as a target, this could be a problem if he died in the Battle for Whiterun as part of the Civil War, which almost always happens. It's possible that it's on his corpse in the Hall of the Dead, but this has not been confirmed.
 * Brand-Shei may be a target, which is also a problem considering he is put in prison when the quest to join the Thieves Guild is completed, so he may be hard to get to. Unless, of course, the necklace is dropped at the start of the Thieves Guild storyline, which would still allow the quests to continue.
 * Any named jewel acquired during one of these missions, such as Lygrleid's ruby can be used in crafting jewelry. The jewel's identity and stolen flag are lost.
 * If the target is a follower of the Dragonborn, the quest is significantly easier and does not require pickpocketing to be done to acquire the quest target.

Bugs

 * The removal script will not always take the stolen ring/necklace/jewel but any ring/necklace/jewel of the same type. For example, when attempting to turn in Garvey's Gold Diamond Ring, it will remain in your inventory and a Gold Diamond Ring that you've enchanted will be removed instead. A workaround is to drop any other items of the same type from your inventory in order to ensure the correct item is removed.
 * Another possible work around would be to change the name of your jewelry once you enchant it, so that it doesn't have the same name anymore. Can't guarantee that it would work, but it's worth a shot. Just added a space to the front of mine when i enchanted them, and I haven't had any issues (note: renaming enchanted jewelry does not prevent them from being removed on the Xbox 360 version.)
 * Hafjorg's Flawless Emerald has 0% chance to pickpocket even with item and potion boosts. This is also the case with Hermir in Windhelm and her jeweled necklace, Kodlak Whitemane's Gold Diamond Necklace (PS3), Omluag's Silver Emerald Necklace (PS3),Sabine Nytte's Silver Sapphire Necklace (Xbox 360), Tacitus Sallustius's Gold Diamond Ring in Markarth, Aval Atheron's Emerald in Windhelm, Silda the Unseen's Diamond in Windhelm (Xbox 360), and Ghorza gra-Bagol's Flawless Emerald in Markarth (Xbox 360). There seems to be no concrete solutions to this bug so far on PC version.
 * This bug appears to occur on other randomly generated quests and NPCs in this quest type across all platforms, regardless of character attributes and skills. Some of the NPCs are also unkillable, thus breaking the quest type because the item cannot be looted from the corpse. As the scripting is not well understood, it is unclear exactly what triggers the bug.
 * (untested on other platforms) A possible solution is to use paralysis poisons or spells, or the Ice Form shout to obtain the item. If you sneak and rapidly press the action button/key you'll gain access to their inventory just before they stand back up, and the item can be stolen no matter what. Using the Paralysis Staff on Silda the Unseen in Windhelm (for her Diamond) -- no bounties added for the assault or the theft even though she cries out "Help me!" after the theft. -Confirmed with Ice Form shout on Fralia Gray-Mane (For Gold Diamond Necklace) on second attempt while sneaking and target sleeping, target returned to sleep with no hostility or bounty added.
 * Tested the Ice Form solution. The target will become hostile and will take damage while frozen. Your follower will attack the target if he/she is nearby, killing the target. Park your follower far enough away to avoid this. While the target is standing up the inventory will be accessible. Use the Ice Form Shout while sneaking with your weapon drawn. The target will freeze and take per second damage while frozen. Provided the target has enough life, the target will thaw and begin to stand. Access the inventory and loot the item without penalty. The target will either attack you or flee. Either way sheathing your weapon at this point will drop the aggro. Collect your follower and go complete the quest.
 * The first fishing job given will sometimes say to "Retrieve Brand-Shei's Jade and Sapphire Circlet from Brand-Shei in Riften". This is incorrect, it should actually be Scouts-Many-Marshes's Jade and Sapphire Circlet in Windhelm. Not a common bug.
 * Retrieve Tythis Ulen's Amethyst from Tythis Ulen in Riften. NPCs (including Tythis) are still standing in the market where Brynjolf causes the distraction in order for you to steal out of the lockbox when trying to join the guild. Tythis is standing in front of a Riften Guard and other NPC. Pickpocketing him is bugged because you get caught. They stand there all day/night staring at nothing.
 * Retrieve Nurelion's Ruby from Nurelion in Windhelm. Bugged, as he is sleeping and Dying. You can't pickpocket him with that being the only message available. He is never awake it seems. Only thing to do is abandon the quest and go for a new one.
 * Occasionally the item requested by Delvin is not on the person. Try saving the game and reloading.
 * Some fishing jobs may require stealing an item that has 0% chance for removal, which in turn will have the quest automatically fail.
 * Solution: Reverse pickpocket a paralysis poison with the Poisoned perk and steal it while they're on the ground.
 * Solution: Give up the quest for something new.
 * Solution: Use the Unrelenting Force shout, and pickpocket while the target is down.
 * Enter the console (press "~"), click on the character to get their ID, enter "showinventory", find the ID of the item you need, and type "drop  1". Pick the item up off the floor.
 * If Nurelion is the target and the White Phial quest has been completed, a message saying "Nurelion is asleep and dying" comes up when trying to interact with him, thus making it impossible to pickpocket him.
 * Use the console and type

Der Diebstahl Рыбалка (Skyrim)