I don’t understand why the post of @TheGreatPython is nonsense. Because there is actually logic behind what he is saying. And I don’t understand why PSG cannot sell Mbappé. I think they are actually willing to sell him because if they do not sell him right now and there is actually no contract extension for Mbappé with PSG, they will have to let Mbappé go as a free agent. That certainly is not going to be the best business for PSG. But I also agree that it is not going to be a good business for Real Madrid to bring him for so much money right now.
Damn. Friend, are you kidding? Mbappe is not a thing and PSG have no right to dispose of him. They can only demand the execution of a contract that expires in a year. Clubs do not "sell" players, they only take compensation for the premature termination of the contract. If you do not know this, then it is surprising to me why you write in topics about football.
So it's basically the same thing right? I see this as a form of business which contains money being transferred for the services of a player which is obviously the 'salary' of a player. And the compensation you are talking about is agreed by both clubs because the club having the ownership of the 'contract' of the player (not the player himself) is willing to terminate the contract prematurely.
In short, buying and selling.