I got a quest called Summerset Shadows which gives me a fence in Windhelm (Niranye). My boyfriend is trying to get this quest too since Windhelm market has all the crafting tools and is very convenient, but he can't get Tonilia in the thieves guild to give him the quest.
We're both guild masters of the theives guild. I thought it might be # of quests done for the thieves guild (I had 17 at the time), but he has gotten the same amount done and still no quest.
Best Answer
Windhelm, Markarth, Solitude and Whiterun all have "influence" quests that each become available once you've done 5 of the randomly-generated jobs from Vex and Delvin in that city. Since jobs in Riften or cities you've already completed do not help your progress towards completing the influence quest, you can save before taking a job from Vex or Delvin and then reload until you get a city you haven't completed yet, if you feel so inclined.
Completing the influence quests unlocks fences in Markarth and Windhelm, but most importantly, each influence quest you complete increases the available gold pool of all fences in the world, up to 4000 once all quests are complete.
When you've completed all four influence quests, plus the main Thieves Guild storyline, you can become the guild master, receiving a significantly-upgraded suit of the guild armor you gained when joining.