I had a colleague who works for a pet rescue tell me that she would never bring a dog in for grooming at Petco or Petsmart. She spent all day there photographing pets with Santa and said the things she saw she would not do to a pet.
We found a wonderful groomer through suggestions from other Yorkie owners at the local Yorkie Meetup group (
www.meetup.com/yorkies). This groomer works out of a veterinarian office, so we figure she can't be abusive or too harsh. Our little Pookie hated grooming until we brought her to this one. She's young and Pookie loves her. They both act like long lost friends when we bring her into the office. Pookie gets so excited and dances around and licks her, so we guess the experience isn't too bad for her.
So you might try going to a meetup or two and ask the other members where they go to get groomed. If it's a bigger place, make sure you get a specific name of the groomer.