Just a word of caution, if you are considering a Border Collie. I don't know if you have young children, but if so, then a Border Collie might not be the ideal choice as they can frequently nip at youngsters, especially when they get excited. It's not aggression, it's just their herding instinct.
If you don't have youngsters, then I'd get several Border Collies!
You've already highlighted the key areas to investigate, I think.
Walking:
How does the dog respond to being walked? I'm afraid that I would walk away if I couldn't walk an adult dog before taking it on. There are so many problems that be identified during a walk. For me, it's like test-driving a car.
Commands:
Does the dog respond to simple commands, such as sit.
Touch:
Can you, or the handler, touch the dog all over the body without any adverse reaction.
Nerves:
Can you clap your hands together without the dog bolting under the nearest desk. A dog with weak nerves can be as bad as (if not worse than) a dog with too much nerve.
Health:
Does the dog have any long-term health disorders, such as epilepsy, partial blindness, hearing difficulties, arthritis, and so forth.
It's important to remember, when visiting shelters, that dogs are rarely showing their true selves. They are often wound up with excitement, frequently barking from frustration, and can be hyper when they leave the kennel. Or they can be the exact opposite and just sit there depressed. I think that you do have to sort of factor this in to the overall equation.
Remember too, it's likely that any adult dog you take on will have at least one issue. The question is which issues can your lifestyle deal with. For example, I work from home all day, and so separation anxiety is something that I would be willing and able to accept and work on. I don't have children and so an excitable dog wouldn't be as much of an issue to me as it might be to some others.
Hope you manage to find the right dog for you though. Though, I'd be willing to bet that it finds you in the end.