I'm using Google Docs to host a simple survey and I noticed that the same person can keep filling out the survey over and over again.
How do I stop users from doing the survey more than once?
Is it possible to block multiple survey responses per user?
Best Answer
Nowadays there is a inbuilt feature: Simply enable the "Only allow one response per person" in the "Form Settings".
The downside is that each user needs to login with their Google account (which they might not have, or they might not want to use).
Source: http://www.labnol.org/internet/prevent-multiple-form-submissions/28675/