Okay, so In order to become thane of Riften, you must first clear out cragslane cavern of skooma dealers. However, if you've visited the cave prior to acquiring this task, eliminating the enemies there does not update the quest objective, making it impossible to complete the quest and become thane. Bethesda should address this major bug in an upcoming patch.

According to http://www.uesp.net/wiki/Skyrim:Supply_and_Demand, it can be triggered to complete if you clear the cavern three times. It takes 7 bandit kills to make the quest complete, but only three bandits spawn at a time so return several times and it should finish.

Alright, thanks, I'll try this out and see if it works.

The major bug they should fix is not having the NPC that starts the quest get killed off camera with no work around like the one mentioned above.

Bump, I'm pretty sure i've killed more than 7 at this point, but the quest still has not been completed.