What really helped us prepare was the class at the local kennel club. It was just a regular obedience class but a bit more serious one than Ive seen elseware. There was no puppy kindergarten aspect to it, the instructor called mid week every week to see if we had questions or problems and was very approachable. I have a hard time with heavy handed dog teachers or the ones who just want the dogs to socialize well with other dogs so had no problem with her methods. We were a good fit.
I think the reason they want a dog to do ok when left with a stranger is so they will handle it if the vet has to take them in the back without the owner or if the dog has to be away from the owner so the owner can carry stuff out to the car with both hands etc. The dog has to be on a leash held by the instructor and out of sight of the owner for 3 min. so it's not as bad as it sounds. During the test the dog can act nervous, just not freak out. Maybe they also want to make sure the dog is secure emotionally on it's own short term, Im not really sure.
I would recemend getting a CGC to every dog owner. It can even lower some dog owner's home owner insurence rates. I know that's why the rotti owner tonight was doing it, along with the great feeling of pride in a well behaved companion.
We just went for vanilla icecream, I didn't want to over do it with the doggy tummys.