Alves' termination is nothing to do with his agent, Beppe said he didn't want unmotivated players here. He's 34 years old and worth next to nothing with a year on his contract.
Agents have the power to advise players to make immoral, poor sporting or greedy decisions. Before the clubs and managers/directors decided the terms of transfer fees or if a player was even to be sold, somewhere along the line agents became more and more powerful, probably because of the influx of money and increased competition for the same players, allowing agents to build up empires and stables of players and become rich and influential enough to play clubs off against each other. Now you either play ball with them or you lose access to top players.