Can you stay? That's what I did with Lexi, the first time.
I know that dogs might tend to "act up" more with their people there than they might if their people weren't there, but... I have to say that I am glad I stayed because although there was nothing outright horrible, I didn't care for the experience. And I always wonder if things would have been worse if I hadn't been there...
I didn't leave Lexi with her second groomer, but she came recommended, and she breeds and shows Yorkies. Also, in speaking with her, I was happy with the things she said. They made me feel comfortable in leaving her there, although there was a big part of me that wanted to stay. It ended up working out really well, and Lexi is so much better about letting me brush her, and I can actually get in a topknot every day - without being punctured by little canine teeth (double)!!!
Either way, I hope it all goes well for you.
