So I seem to have a problem making TG quests work in Raven Rock. First Delvin sent me there on a bedlam job but nothing I stole counted for anything (and I cleared out that one rich family's house). I had to quit the job. Now he sent me to pickpocket a diamond necklace of someone who is busy building Miraak's stones. With all my gear and potions, everything he has on him is 90% chance successful steal, but the necklace is 0% and he always snaps out of his trance and catches me. Is there any way to make this work or should I just always refuse the Raven Rock jobs? My PP skill is 55 with 3/5 Light Fingers.

Diamond necklaces are rather expensive, that could be part of the problem.