people can only enter information one time

Hi. I'm having a problem with people using forms more than once to order things. It seems that if someone places an order one time, they can never use that same form again at a future date, it locks them out. Is there a way around this or something I need to do in the settings? I've tried to figure it out. I have gone back and deleted their submissions to have them try the form link again, and it still won't work for them. I'm not sure how to resolve this other than to continually create new forms for people to use, which is not productive, obviously. Thank you for your help.

I suggest you put a captcha field in your form. It will make every submission unique so they can submit again.

Don't hesitate to reply back if it does not solve the issue.