This is probably my biggest isse with the game right now. For instance I bought Juan Pablo Herrera for cheap, then 7 months later I get bid for 400k and my chariman forces me to sell, eventhough I'm well on profit side and he was my best player.

And there's nothing I could do.
I wish they added some feature and fix for this, because it's very discouraging to even go out there and try find some talent, because you always have fear on your back that your chairman will sell him very soon. It'd be acceptable and all good if chairman would be more patient and force on real big money offers or when club finances are poor, but when finances are good, player is one of your key players...then selling this player for bargain price is pretty silly in my opinion.
I'll add another suggestion on this issue: Maybe on very rare occasions when you have done well and all that and it's contract renewal time and your board obviously wants to keep you...you could add some kind of
Absolute freedom ( regarding player deals within the budget clause on your contract, which would mean board would let you decide these things.