Currently, the way steam family works is that when you play a game through the steam family, it adds the hours you play of that game to your account. this means that, if you buy the game at some point in time, if it is, say, on sale and you buy it with all the DLC because your family member does not own the DLC, you will now not be able to refund said game. this is because the hours you accumulated before purchase will count for the sake of seeing if a game is refundable or not, and the automatic system will not refund the game due to perceiving you as having too many hours

this is ESPECIALLY an issue if it is a bundle - for me, I played some Old World - gaining aproximately 18 hours via the steam family. I then wanted to see how the DLC are and how much they truly add to the game, so I purchased the entire bundle - since it is cheaper. however, because the main game counted as unrefundable, and the purchase was one entire package, it meant I could not refund a single item from the list that I bought - including all the DLC.

it was luckily resolved via contacting steam support (which also directed me here to make a suggestion) however it should be resolvable via the automatic system as well preferably to save the time of employees and the buyers alike - as the current refund system does not quite work as intended, and needs to be able to differentiate between hours played before, and hours played after purchase. because if it was not for steam support I would now have 50 Euros less.