Our company offers product training subscriptions to our customers and partners and we are in the process of implementing PayPal to enable self-serve purchasing. We discovered through testing that a user is able to purchase a subscription plan multiple times which puts both us and our customers as risk of losing revenue, increased administrative tasks and an unpleasant experience for both sides. Ideally, when a user purchases a limited time subscription, they should not be able to re-purchase the same item until the initial subscription expires. The system should alert them they are already enrolled in an active subscription and not allow them to proceed with adding it to their cart.

Overall, I think subscriptions need a little more love! They are a very useful tool for our company to help our customers get access to the training they need with little friction.