I think a well-trained dog is one that is so well bonded to its owner that the owner can expect the dog to perform any command (that the owner knows the dog knows) in any environment. And the dog will.
A well trained dog, might also perform the commands for people other than their owner.
Rushie was well trained in basic obedience. He was titled, had his CGC, and a therapy dog. When I sold him, he was four. A person that I often trained with, but not the trainer, who had never handled the dog before, was able to take the lead and show the prospective owner, that the dog could indeed do the various commands. And he did them.
This lady was a dog-person. She was raising, showing, training, breeding dogs forever. They asked her to give a demonstration one year at the fair. She agreed. She got to the place with the dog, and then without any warning or preparation, they told her they wanted her up in the press box, and the dog down where the people could see him perform his tasks. She had never done anything like that with the dog -- never commanded through a loud speaker. But she was game, and did it.
The dog came through for her perfectly. It was a well-trained dog.
I think everyone's level of expectations for their dog's behavior/training is different. Where I might consider my dogs well-trained, another might see them with limited training and that being shoddy. So I guess it really doesn't matter what we consider "well-trained." You need to define this for yourself and your dogs.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC