[Resolved] Trial Period

Not to be facetious, but here is an actual “real world” version of what I think you are concerned about…
For the last 70+ years, my mother has been getting the special “introductory offer” subscription price to the Los Angeles Times newspaper. All she does is simply let the existing subscription run out, and then resubscribes using a different variation of her name and street address. The point is, there is going to be no foolproof way of preventing situations like this from happening.

The most practical thing you can do is create a TOS (Terms Of Service) agreement for your members. Someplace in the agreement, state that trial subscriptions are for new members only and that you reserve the right to cancel a membership if fraud is detected.

Subscriptions can only be “renewed” if the member is logged into their account. You’d use partial content protection to only show subscription purchases that include trials, to visitors who are not logged in.
https://simple-membership-plugin.com/apply-partial-section-protection/

If an existing member tries to purchase a subscription that includes a trial, without logging in, SWPM will think it’s a new account signup; and will prevent them from using an existing user name or email address.

So… if my crafty dear mother were to try cheating this system, she’d have to have a supply of “burner” email addresses, PayPal aliases, and user names. Doable, but not worth the hassle for most people.

If you are offering a fully free option then you can’t really stop a determined user from signing up again (as mentioned by @The Assurer already).

The way to stop this is to offer a paid trial option. You charge an small amount for the trial. That should deter users from doing this. This is one of the main reasons why some businesses offer paid trials.