Just to clarify your answer, a bit.

If there is play, using Whilst's technique, make sure you are looking at the play in the ball joint, not the wheel bearings. in other words, have someone else shake the wheel back and forth while you carefully view the ball joint. If it is warn, you will see the play, clearly.

In reference to your original question, there is no way to directly, visually see if a ball joint is bad--unless it is really, really, really bad (like broken).

Use Whilst's technique.