One return, and whichever decision is due on it. The page changes with the state — you can't refund something that hasn't been sent back, so that button simply isn't there yet.
The header
The RMA code, the state, and a link straight to the order — worth following before deciding anything. The order tells you what was paid, what has already been refunded, and whether it ever shipped.
Customer and reason
Who asked, and their words, not a dropdown. This is the whole of your evidence — "card arrived with a bent corner" is a different decision from "changed my mind" — so read it before approving. Nothing is edited or categorised on the way in.
Items
The lines they want to send back and how many of each, from the original order. You can't change the quantities. They asked for specific items and the decision in front of you is whether to grant that. To refund something different, decline this and refund the order directly, where you can set any quantity you like.
Once it's finished
An Outcome panel replaces the buttons: what was decided, when, how much went back, and the reason you gave if you declined it. There is no undo. If you get one wrong the fix happens on the order — refund more there, or take the goods back in as a normal sale.