I used to work at Petsmart and you could see the groomers working on the dogs and cats. Usually what they'd do is two people would work on a cat, especially if it's one to be shaved. So, while one person holds the cat down, the other shaves away. They usually hold it by the back of the neck and will talk to it, pet it, whatever. I had been told by them that when a cat is upset/nervous/scared, they will sometimes pass gas (or something similar). In other words, the groomers have seen it all. I'd recommend a lion cut, too. The groomers should be more than happy to take care of your cat.
I remember one customer brought his cat in like every 2 mths. or so. The hair under the armpits would mat as the cat walked, so no amount of brushing helped that problem.