How do I prevent a user from submitting multiple survey forms?

You can set a Unique Submission in your form. This will prevent multiple submissions from the same IP or same browser. Here's a guide: How-to-Set-Unique-Submissions-on-a-Form

You may also set a Unique Question so that the same value entered in the field will not be allowed to submit anymore. Here's a guide: How-to-set-Form-Limits-Based-on-a-Unique-Question

Hope this helps. If you have any questions, let us know. Thank you.