ok how about a profit share to the former owner, like this, if a bought player gets resold within a season, the former manager gets 50% of the tradeprice, that would make daytrades nearly impossible?
or the former owner gets 50% of the profit, that might would make both sides happy and the former team does not loose much if a player might gone for a to low price and daytraders would have more friends coz they make profit not only for themselfes no more, like everybody is happy when a daytrader bought their players?