If the dog if with the owner, he is with his pack, its make a huge difference, the dog first see your reaction for take his own reaction agains the helpler, if you're calm why would he be scary? You won't be able to see real character of the dog in this way even a shy dog will have more courageous reaction than normal. It's like you test the character of the dog in his own territory.
Surelly a really problematic dog will show his problems even if the owner is at side, but you won't be able to evaluate the real character of the normal dogs
