Well, that depends. The faster trainers will keep up for awhile... I tend to keep my players for a least a few seasons. When they are three stars, and no chance of gaining back the fourth, I think about selling them. It's not just the stars, its how you have applied the points and how you utilise the player. If they produce, who cares what their stars are.. I know a couple teams with 2 star guys that still get 8 ratings, and Man of the Matches!