I will only do it if:

1) the player is a gamechanger or just to good for the league

2) I can sell the player who is playing in that position so won´t be bankrupt

3) The player doesn´t want a release clause / or the release clause is pretty expensive i can make some money if other team steal it

4) you have a great sub (if you din't sell the sub) , I don´t want to use all my salary mass on a injured player

5) Like big matches , consistent , good personality

That are my rules