I've encountered a bug with the second thieves guild quest (Taking Care of Business) which is preventing me from going any further through the questline. After collecting the money owed from the three people in Riften and taking it to Brynjolf in the Ragged Flagon he tells me to follow him and walks to the cistern. Unfortunately, when I enter the cistern Mercer isn't there so the next quest doesn't start and everyone starts attacking me with the same dialogue used when trespassing.

The Wiki shows a workround using console commands to join the guild and start the Dampening Spirits quest which would let me continue but it doesn't get me the quest rewards from Taking Care of Business such as the guild armour and the ability to use Tonilia as a fence. As I tend to steal anything in the game that's not nailed down I really need to use her as a fence.

I have only had this issue since patch 1.9 was released but since then I've tried on 3 new characters and had the same issue with each.