This is what some people have been suggesting since page 1 but the problem I see with that is you are describing the “You’d be able to get your money back at any point for any reason and keep using the content” would be the one option on the UE4 marketplace that makes buying easier and happier experience. Not the 24/7 support, walkthrough, bug fixes and updates which are currently provided by every one of us.
Additionally, if purchase rates go up based on just that statement then it’s only a matter of time before almost everyone get’s their money back. Sellers do not live with high purchase rates. They live with how much of it they get to keep in their pocket. It’s a trade and reverting the trade is never an option unless both sides are happy with it.