Paypal is BS in these situations. If you can't provide proof of delivery YOU LOSE.
The only work around is to give something physical with the membership that you mail to them where you have tracking info. You have to prove they received something. Even if its just a thank you note.
Is there anyway to know how many times someone paid for a subscription?
I have a forum that has both free and paid memberships, what I want to know is can I, through IPB/Nexus, know how many times someone has paid for membership