It should be easy enough to implement a refundability window based on either time-in-game or percentage completion (based on main story line, not side quests and diversions).

I mean if the game says 20 hours of gameplay but you complete it in an hour, that's false advertising and there should be an exception. But if a game says it takes an hour to complete and you complete it in an hour, there's no reason why you should be able to get that refunded.