I'd ask them to walk you through their puppy raising program. If they use a particular program, and if not, how they're introducing puppies to novel things and helping them learn about the world. If you haven't already, talk about what they focus on in their breeding program, and how they're trying to meet them. You can ask about their lines, too. What's typical of their dogs, what's unusual, how their lines compare to the temperament and health of the breed at large.