Rather than worry about questionnaires for candidates who don't accept your offer, concentrate your efforts on fixing the recruitment and interview process to raise the caliber of applicants. Also, make sure you are offering a workplace that people WANT to work in; i.e., offering advancement, job fulfillment, decent salary, etc.
Improving the Interview Process
Your interview process should be able to weed out those only interested in money and nothing else. Secondly, no one is going to bother filling in a questionnaire. Would you if someone sent one to you? You're too busy starting your new job with another employer to worry about this nonsense.
Understanding Candidate Rejections
If you are concerned about why people don't want to join your organization, then pick up the phone and TALK to them. Develop four questions to ask, and don't waste either your or the other person's time with this. A short, sharp conversation and end the call. Many people won't want to discuss it with you, so be prepared for that. Also, be prepared to be told things that I suspect YOU WON'T WANT TO HEAR.