I do not believe that a case has been made that the listing/continually relisting players is causing a competitive imbalance that requires an additional mechanic to disincentivize it.
I've already made this suggestion 2 or 3 times:Every time a player is not sold, the fees increase. An example, if you sell a player that you have in your roster since a long time you will get 97% of the price. if he's not sold, my suggestion is to decrease 97% to 92%. Then 87%, 82%,...Joe