Membership free trials – can someone keep signing up for free trials?

There is a bit of mixed messaging going on here, in this thread: Brian seems to imply that members cannot abuse free trials but in this thread: Aristath says it’s something that you can’t stop.

So please can you be clear with me here:

I have a free trial period on my website, 14 days finite and then it automatically kicks into a monthly payment plan.

I also have an annual plan with a similar 14 day trial.

Is there any way to stop:

1) A user just cancelling their trial account after 13 days and then signing up to the same free trial again with the same PayPal account?

2) A user cancelling the monthly free trial after 13 days and then signing up to the annual free trial for another 14 days free?

3) A user deleting their account and creating a new one, using the same PayPal account as last time, and getting lots of free trails.

If there is nothing preventing this then it really removes the whole business model of having a free trial from being viable. Aristath recommended somehow limiting the free trial so that people need to become real members, but this is a problem because then every member would have a limited experience for the first 14 days of their subscription, which would not encourage them to sign up to the full account!

If there isn’t already there should be a system in place that keeps track of PayPal email addresses and stops people getting free trials multiple times.

Please let me know if this is the case, and what you are going to do about it.