I'm very skeptical when I hear horror stories. I've been grooming professionally for over 4 years now. I've been working out of my house for a couple of months now but before that I worked at the busiest grooming parlour in the valley. One year we were doing 40 dogs a day and 60 dogs a day in the winter time, and became known as the place to deal with "problem dogs." All of the vets in town recommended us for senior and difficult dogs. We had people fly in their dogs from Alberta and Washington.

And even with how busy we were and how many thousands of clients we had, many people still said bad things about us. Our building was torn down in May due to someone buying the land to build condos. However, many of our clients heard from other people that it was because we "had to shut down because we are too abusive." It's sad to hear things like this, because we dealt with some really difficult dogs who were kicked out of several other parlours in town, and really had to work with them to make them good.

Of course many people would walk in the door just as a dog was screaming and assume we were beating it. Unfortunatly many dogs put up a huge fuss for nail clipping, blowdrying, ear plucking, etc. We've done dogs that could only be done when they were completely put under at the vet, and we absolutely refused to sedate any of the animals, so yes, every day we dealt with dogs that screamed and bit and basically freaked out because they had a rough start somewhere else, were genetically strange dogs, or were very old and senile.

So not every groomer is bad just because of something you hear. We've heard things over the years from our clients that we just had to laugh at. Literally hundreds of times we heard how "the last groomer just shaved him off for no reason." 99% of the time, these are dogs that are consistently matted, and we absolutely tortured some poor dogs dematting them because their owners swore up and down that the dogs were not matted, and then they wonder why their dog is so afraid to come in to be groomed, so they think we must abuse it.
And, groomers make mistakes. Every groomer has cut dogs. It just happens. The dog zigs when you zag, the dog pushes itself into the blade while you are scissoring, etc. Sometimes it's the groomer's fault, sometimes it's the dog's fault. Sometimes dogs fall off tables. Sometimes they literally try to. I've had dogs fling themselves off my table while I'm working on them and I'm surprised they didn't break their neck. A dog shouldn't be left on a table unsupervised. You should always have someone there to watch if you have to leave your table. One time, I was grooming a malamute and the front legs on the table buckled and the whole table collapsed, I literally leapt forward to try to catch the dog so it wouldn't hit the ground, and instead was pushed to the ground by the dog and I landed on both of my elbows. Of course there had to be clients in when that happened. We didn't know the table was broken.
And old dog fits...basically an older dog's heart will skip a beat and it's almost like they have a seizure in their mind. They just start SCREAMING. The only way to stop it is to hold the mouth shut so it can't hear itself, and turn off all noise. This usually happens during the blowdry. It looks like we're torturing it..it sounds like it... but if you don't hold the mouth shut while it screams, the dog will literally scare itself to death.
So sometimes not everything is what it seems. When you deal with problem dogs, old dogs, and new puppies on a regular basis, it can seem very chaotic. But we loved the dogs and we did our best with them, and when people would say bad things, we knew it was because we were doing some difficult because we never hurt a dog on purpose.

On the other hand, there are bad groomers, plain and simple. I know from co-workers going to work elsewhere. One lady in town gets high on crack before she grooms. She kicked a small dog down the stairs. My co-worker saw this. Another lady lets her big dogs run loose with her client dogs, and occasionally they will attack the client dogs. She was seen kicking a chihuhua across the room. Two of my co-workers saw this.
And the rest I hear is just rumors, so not sure if it's true. I have heard that one lady leaves her dogs on the table to stand for hours at a time with no break. I know of one place that broke a dog's leg, and one place that got so much water in a dog's lungs it was in pretty bad condition for a while, coughing up blood, etc.
You'll hear horror stories about every place, you just have to make your own decisions!