All refunds are handled through the marketplace staff. The method employed for countering the 30% loss is to limit the window in which you can refund an item, IRC it is a week or two after purchase. That way the money earned wasn’t paid out, and can be subtracted if necessary. What you’re proposing is very little good and a whole lot of bad. It gives zero protection to the seller, and I can tell you without a doubt if the marketplace returns to that policy I will be forced to remove my products and I know I probably wouldn’t be the only one. We already have enough with external piracy, we shouldn’t have to be subjected to random refunds for reasons that are beyond our control or nonexistent because a buyer wants to get a free package.
No one is denying that reviews and ratings are critical to the marketplace experience. However your suggestion that you leave a bad rating/comment if your refund claim isn’t justifiable in accordance with the existing policy and is subsequently denied is essentially extortion. Having dealt with that situation personally, I can tell you the marketplace staff takes that very seriously.
The official policy doesn’t explicitly state a seller can request a refund, but it doesn’t mean that we can’t. I’ve seen some sellers who opted to give refunds even though the claims weren’t within the policy’s parameters. As far as I’m aware Epic does have a system in place which does that, however it is exclusive to them. UE4 Marketplace sellers are given very little information in comparison with other marketplaces.