So I just got done beating the main quest line for the Thieves guild and I didn't get this Achievement. So I started to look around online some people say you have to do over 40 side jobs with them but I've done a lot and still no achievement, but then I notice the lady you can sell stolen goods asks me to turn in one of my guild armor well I sold it all and I can't even sell or buy anything from her! Some one said to get the achievement you have to turn in all your guild armor for the better armor and then achievement will unlock! I do not know if this is true or not but if it is this sucks for me unless anyone know where to find some more of the thieve guild armor? Just giving people a heads up don't sell that armor it might make this glitch happen. I'm going to go ahead and do more side jobs hopefully it will unlock if not I will have to get it with a other char.