As for human products on dogs, I would rather use something made specifically for dogs and coat type. Besides, by the time you spend the money on some of the higher quality human products, you can buy some GREAT products for dogs.
There are coat specific products (ie: drop coats, curly coats, etc) that are formulated for a particular type of coat. Poodle coats, for instance, need to be wirey for the best results when clipping/scissoring. That's what they coat is supposed to be like, not, soft. Using conditioning shampoo's and conditioner on a poodle, will make the coat to soft and limp and you'll never get a nice finish. Also, human products tend to build up on the coat, which will eventually make the coat harder to work with.
I use Isle of Dogs on all my curly and drop coated dogs, it can't be beat by any other product, human OR dog
If there are groomers bragging about using human products on dogs, then I'd probably steer clear if I was a client looking for a groomer. Chances are, they are willing to use other off-label products (like dish soap) as well.