How can I avoid receiving a double submission.

I have customers that make a submission and i receive it and within a few seconds or minutes the exact same thing comes through again.  Are my customers doing some on their end that is causing this and can I fix this?

You can enable the Unique submission feature on the form.

User guide: How-to-Set-Unique-Submissions-on-a-Form

It is possible also that your form was compromised by spam the reason there are now spam submissions.

You can also add the Captcha field on your form so that it will require captcha validation before the form can be submitted.

User guide: How-to-add-a-CAPTCHA-field

Hope this help. Let us know if you need further assistance.