well...it depends on the player..if he is one of my star players i reject his request...still play him..and hope that he will get over it...if he is one of the subs...i'll let him go...but at a price...
Like Bongo-Bongo said, it really does depend on the situation.
In FM 2007 and I think in FM 2006 I made meaty profit. I try to keep the talent but sure can't half be a money spinner, got millions for some Colombian player.
But more often than not I loose, player is still unhappy that I've asked them to stay they move on disappointed.
I always to try to pick the best sounding answer not to cause any unessaccary aggravation.