Hi Danna,
I think it depends a lot on the needs of your pet(s). You'll be answering a lot of questions about their routines and habits, likes and dislikes, etc, but if you feel the sitter doesn't hit on a topic that's of particular importance to you and your dog, speak up. You know your pet well, and the sitter does not, so go in ready to talk about their weird quirks, food preferences and restrictions, kinds of trouble they tend to get into, and the things they really enjoy so the sitter gets a good picture of how the stay might go. I find that while I'm asking a lot of questions about the dog, most of my clients just ask basic questions about me - what I do for a living, how long I've lived in Portland, how long I've had my dogs, how long I've been sitting, what my experiences have been like, etc. I think these are good questions to ask. Even if the specific answers aren't that important, it's a good way to judge the character of the person you're leaving your pets with. If someone had only bad things to say about their previous clients or rover guests, I'd be wary of leaving my dogs with them. Remember, you're interviewing each other, and this is a person you're going to trust with your family members. You want to know that someone is capable, but you also want to know that they're personable and professional.
Hope this helps!
Laura