Pre-populate your answers.
Help respondents you know by filling in answers to the basics. Send out your surveys with Zoho Campaigns or Zoho CRM, and respondents will be able to see their information pre-filled in the survey. The information would be taken from the Zoho CRM and Zoho Campaign database. You could even have answers filled with information grabbed from the URL. You don't even need to ask your respondents for their details. As long as your contact's information is stored in Zoho Campaigns or Zoho CRM, you could know who responded to your survey.