Please add a feature where you can toggle on/off allowing a customer to purchase a product only once or mutliple times. Somehow, customers are clicking the button twice and accidentally purchasing some products twice, then asking for a refund later for their duplicate purchase (thinking we charged them twice). This is costing us unnecessary money from the merchant fees everytime they purchase. This particular product is a course they will only need to purchase once so it would make things very simple if I could limit them to one purchase and avoid their inadvertant multiple purchases