This is where the "value at the end of the window" seems to fail for us.
Teams know we're desperate for a player but often they don't seem to be desperate to sell.
Leaving it to the end of the window also often just means the selling club don't have time to spend the money we're offering them on a replacement.
This tactic will only regularly work with selling clubs that have a surplus of players, a player on strike or are in financial trouble.