@Fuseteam Yes, you are right. The transaction is directly between the wallets from the user and the developer, but it would maybe be good to implement a system that ensures that the user can ask the developer for a refund (for example a button that appears after the payment).
Maybe it would even be easier to have a system where the user can use the app for free for a certain amount of time (the time he would be entitled to a refund) and than the user can decide to pay for the app, if he wants to get future updates.
This is of cause very theoretical, because with the feedback I got so far, I don't think the majority of users want any form of payment system.