My daughter is a dog groomer & yes she does express the anal glands!!!!!!
I would say for the work she does on most dogs, more people should tip. I have seen her come home from work covered in dog hairs, scratched up & many times bitten. I think back years ago when I use to go to a dog groomer, I did tip her, but I wish it had of been more, now I see the other side of things

I always pay $25 for my little dog to be groomed every 5-6 weeks, and i tip her $5 each time. When it gets close to Christmas I always tip her $10.

I also always try to do her a favor and brush the knots out of my dog's hair before i take her in.

And as far as i know, she does the anal glands every visit, so it is worth every penny i pay her.