With just about every purchase in the App Store, all sales are final. You do not get to create your own free trial by using an app/subscription, then requesting a refund later. Some apps offer a free trial, while others do not. It is not possible to "accidentally" make a purchase as this is not done by just accidentally touching a button. You are required to double click the side button with the purchase amount showing on the screen, followed by verification using Face ID/Touch ID or passcode.
You do have a better chance at getting a refund for an app that does not work as advertised, but even in this case there are other considerations that may be accounted for in making that decision that are not published. Since that is a decision made by Apple, there is nothing anyone here can do to provide assistance.