Dominance theory was retracted.

Motor patterns, not personality. Breed is a weak predictor of traits like friendliness or trainability, and a much better predictor of the sequences a dog is inclined to perform and finds satisfying in itself — herding lines carry heightened stalking and chasing, retrieving lines carry carrying and holding, terriers carry catching and shaking, scent lines carry nose-driven following. That matters because what a dog is inclined to do is what it finds rewarding, and what it finds rewarding is what you can pay it with.

Almost certainly not, and this was taught widely and confidently so there's no shame in having believed it. The idea comes from mid-twentieth-century studies of unrelated captive wolves, and the researcher most associated with it publicly repudiated the interpretation once wild packs were studied and found to be family groups. Dogs aren't wolves in any case. Most behaviour attributed to dominance turns out to be fear, over-arousal, or a behaviour that's simply been reinforced.

They often stop a behaviour in the moment, which is exactly why they persist — and studies comparing reward-based training with aversive methods including electronic and prong collars have found more stress-related behaviour and no advantage in obedience outcomes. Several countries have restricted or banned electronic collars. The deeper problem is that suppressing a behaviour isn't the same as changing how a dog feels, and a dog punished for growling still feels the same and has lost its warning.

Possibly the opposite. A dog kept chronically over-aroused becomes fitter and no calmer, and repetitive ball throwing in particular keeps some dogs aroused rather than tiring them. Adult dogs sleep a great deal, and chronically under-rested dogs behave worse in ways that look exactly like training failures. Sniffing, chewing, a quiet place and a routine that permits sleep resolve a surprising share of complaints — a walk spent sniffing tires a dog more than one spent covering distance.

Carefully, because in most countries the title isn't protected and anyone may use it. Ask two things: what qualification they hold and from which body, and specifically what happens when the dog gets something wrong. The second answer tells you most — anything involving corrections, discomfort or establishing leadership is a reason to look elsewhere, and someone who won't answer it directly has answered it. For fear, aggression, separation distress or compulsive behaviour, go via your vet to a qualified behaviourist instead.