I would keep the questionnaire as a way to rule out potential new owners easily.
Then I would do extensive phone interviewing.
If they can't take the time to fill it out, then they can't take 15-20 years out of their lives to have a dog. I am on the fence about home checks though. We aren't hiding anything here but I still don't think I'd want somebody in our personal things. I know some do it just to make sure everything is secure (fencing, etc.) which is fair but if you are going to sell them your dog, you should be able to trust that everything is as safe as possible already. Just my opinion.
