"Limit to existing clients only" option in products
Option to select "Limit to existing clients only" option in products, similarly to "Limit sign-up to new clients only" to allow exclusive offers for existing clients.
Gul-Reza Tareen commented
Make certain Trainerize pay products only purchasable by existing clients, so that if the link is shared and someone else buys the product then they are not automatically created a client account on trainerize.
Perhaps the way to do this is by having existing clients log in to their accounts before they can purchase the products.