Dogs trained for specific tasks; how are they treated by the owners? (sniff inside)

This question and its answers made me think of this…

I’m wondering about dogs that get trained as seeing eye dogs for the blind, attack or drug sniffing dogs used by the police, hunting dogs for catching wild animals…how are they treated by their owners or trainers? I don’t know much about dogs, and I’ve never had one. How much work does it take to train a dog to do a certain thing like that, and is it stressful for the dog? I imagine it is a lot of work.
I mean, if you want a dog to be obedient and devoted to its task, you have to tap into its nature and, in a way, make him submit to your wants, all the while considering its natural abilities. (hunting, smelling, stuff like that) But for the dog to trust its task, it has to trust its owner. Is that how it works? I suppose the type of dog is also a significant matter, too.

Is it even possible to get a dog to do these things if he doesn’t have a good owner? I’m thinking that a sad, angry or depressed dog won’t answer the call.
So, how are these special task dogs trained, and what are the owners like? Is there a difference depending on the task the dog is trained for? Probably, right? I like to think they’re happy dogs, what say you?

Also, feel free to answer for animals other than dogs that get trained in specific ways. Thinking about circus animals and how they’re not all treated well at all, but are still obedient, for the most part…I also think there must be quite a difference between getting an otherwise wild animal doing what you want, as opposed to a dog, which has lived with men for centuries. What are the differences like?

Also, sub question;
I keep thinking about junkyard dogs, but I think that, often, those are dogs that are beyond repair if you will, and have been abused or mistreated to a point that they’ll never really be nice. Having the dog hang around a junkyard all day is a better alternative to putting it to death, but is that even true about junkyard dogs? Or do they get trained too? I mean the dog can’t make a difference between who’s allowed in and who’s not, right? Especially if it doesn’t give a shit… unless it’s trained.