The likes of SAF or Mourinho have relied heavily on a large scouting network to find players and on club executives to negotiate deals, but the final say seems to have been theirs when it comes to recruiting a player. Is this the case with the DoF?
If a DoF is having the last word, then the potential diasagreements with the manager are self evident. If he is not having the final say, what's the point of having him? He's just a glorified scout.
It ought to be very simple. There should be should be an investment transfer budget on which the DoF has the final say because his job is to make the squad stable in the long run. The coach should have the final say in tactical transfers to correct any short-term deficiencies in the squad. There is no reason in the world for the two to have disagreements because they are responsible for different things.