If you'd been smart about it you would have given him his new contract when he asked for it, trying to save money in that scenario isn't smart. Look at that Portuguese **** at united, new contract every year. Same with Sergio here.
Those two players are the stars of both clubs though. Sterling was a bit part player in that season. I doubt anyone at the club envisaged this kind of trouble from him when they went to him with a contract offer half way through the season. If he had another agent I doubt it would have been any trouble. Berahino did the exact same thing and has the exact same agent.