I felt kinda stupid finding this out after so many times of swapping the soul gems but when Ajirra give you the Bet with Galbedir quest she says to 'place' the fake soul gem in the desk, not to swap it for the one already in there. I never picked up on her choice of words and automatcally assumed she wanted them swapped, it's no big thing but it's nice to know you can still get her services and fullfill the quest.

Most of you probably already knew this but I thought I'd share it anyway.

Huh? She doesn't refuse services if you steal any amount of her stuff - you just can't sell her stuff back to her.