how about having such kind of transfer exchanges??
Similar to the one involving William Gallas and Ashley Cole between Arsenal and Chelsea.

it might take a bit of time to implement, but it does sound good when you can get some money for a player and still be relieved that u have a similar quality, albeit the new one may be a lil bit older or of inferior quality.
And for the buying side also, you get a better player having spent less money at the expense of another player whom you could have struggled to sell…

but we can have more feedbacks about the drawbacks of such a system.
waiting for more suggestions…