First I want ot admit that I did not read all of the responses to the thread, but I am a groomer so I thought I'd tell you what I know.

Our shop does not refuse any breed on that basis alone, but I know that some do. Chows are a very common type of dog to get refused. Chows, even the best tempermented ones, do not like the type of things that groomers need to do. Brushing is especially NOT well tolerated by them. Combine that with the fact that 99% of pet owners do not know how to properly brush their pets, so by the time they come to us it is a long grueling experience for the pet.
Now I don't wish to hear "I brush my dog" or "My dog doesn't have any mats". I hear it all the time and with the matted pet standing right in front of us. Until you've done it PROPERLY you will never know just how much hard work is involved. Chows (and a lot of other dogs too) do not have the patience or tolerence for this. We get ALL of the shedding undercoat out of the fur and if it has been a long time since it was done PROPERLY, it tugs a bit. When they tire of this, they BITE.......YES, they BITE........and you can't tell me that they won't. But it is not only chows.
Like it or not, if we get bit (and a muzzle is NOT always 100% effective) we cannot work, so many groomers who rely on their income cannot take the chance. Many a groomer will not do cats for the very same reason.
So, instead of being insulted just find someone else. If your dog is indeed good, then the groomer that gave him a chance will have a good customer for as long as you take him there.