If refunds really are the issue here then I hope that someone at Valve removes their finger from their bunghole and gets to work on a very simple implementation kind of like the Amazon pre-order price guarantee.
Just make it so every game bought during a sale period is checked against the lowest price between dates x and y and then charge people the lowest price by returning whatever difference as Steam wallet credit.
This would take a doped college kid about a day to code properly. Why can't Valve be bothered with doing the most simple shit? Has all the sugar and fat really paralyzed Gabe's brain to the point of a flatline?