That doesn't really matter, does it? You could have fixed or percental fees in favour of the publisher, depending on the age of the game, for example. They would earn something every time the game is sold on. Would be difficult to find a solution that would be attractive for everyone, of course. It will always be better for a publisher to sell a new game, I guess.
How would that work though? Physically a second hand copy will be a bit battered or dirty or whatever but there would be no real difference between new and used digital games?