E-commerce application how is this robustness criteria implemented?

Consider the following use case 1. User selects a product to purchase on seller's site开发者_StackOverflow社区 2. Clicks on net-banking option and redirected to his bank website 3. Successfully makes the payment. 4. But before the payment gateway redirects him back to seller site the browser crashes. 5. Seller site reports that payment is not recived but the bank reports that payment has been made.

What are the best practices to handle such cases?

Return money to customer or deliver goods. Should be a rare occasion, and I dont really see it possible as automating.

What you could ALSo do is regularly check all open / pending payments from the website (as: the user was sent to the bank, so I can check in an hour whether I simply missed / never got the callback / for the payment.

Imagine 4 is : User closes interface and browser never returns.

The payment gateway should have an API to keep and identify those, including whether the payment was finally aprooved.