Are you a member of the YT SF meetup group on meetup.com? I know a lot of them go to one groomer in the city that I have heard them rave about. You might want to check that out if the city isnt too far of a drive for you.
Have you tried DIY grooming? You can get sheers pretty inexpensively at Ross practice. Granted there will most likely be some mistakes but over time he'll look fabulous and you will save tons of $$$ on grooming (not to mention always have it dont the way you like it).
I guess I am just not very trusting of groomers (or a control freak--probably both lol).
If you do make a boo boo grooming just remember there is no such thing as an ugly Yorkie!