Questions I'd ask:

  - what's the dog's daily routine?
  - what commands does the dog understand?
  - what will the dog do if the leash is dropped?
  - how does the dog react to: cats, squirrels, small dogs, larger dogs, birds, loud noises, children, people approaching, etc?
  - what foods are ok? What foods are not ok?
  - is the dog allowed on furniture? If not, what's the command?
  - what is the dog's tell to go outside?