How to set up a free order option without clients abusing and getting multiples?

We'd like to provide 500 visitors for free, 1 per person, however it will undoubtedly be abused without some kind of restraint.  Ideas?

We also thought of locking some content which would have a $0.00 coupon for the 500 visitors, however the coupon can still be used multiple times.  Ideas?

You can set up a Unique Question form limit, so that one of your form fields will require a different answer in each submission. For example, setting it up on an email field will require that the form is submitted by a different person/email address every time.

This guide explains how to set up a Unique Question form limit:

https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

Similarly to the above, you can even prevent any IP address that has previously submitted your form from filling it out again:

https://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form

If you need further clarifications, please let us know.