Certain elements of a player’s qualities are easy to perceive. How well do they strike the ball? Do they have the body control to fend of attackers? Or, conversely, can they challenge an opposing player without fouling? How fast are they, both with and without the ball?
Then there are qualities that are a bit harder to assess directly but are no less important. How well do they read the game? Can they be as dangerous without the ball as they are with it? Do they communicate clearly and directly with teammates?
But then there are questions that depend on so many different variables that even the best answers are only guesses.