Well, I am a Petsmart groomer hater so if you have no other choice than to take him there I wouldn't leave him alone.
How old is he and is this his first real grooming? The grooming always includes a shampoo so I would take advantage of that for sure. IMO I would let the groomer decided if he really needs to be shaved. They have dematting tools that can be used so he really might not be as bad as you think. Usually, I ask my groomer for the "sanitary package" who of course she knows means the butt and the underside of their body around the private area. If you want the topknot be
very specific that they are not to touch that area. Ask for the ears to be "tipped" and if they need to shave him specify to leave the face long.
Post some pics when he comes home