Do I really need to replace the lower control arm?

[duckseatfree]

So I went to a tire kingdom to get my rotors and brakes switched out (I know but I had no choice and was going out of town). They came back and told me the ball joint was bad on the front left side of the car.

The guy showed me by moving the tire side to side and there was a little play. I was just thinking about it and given enough pressure, you can make anything move.

Is there a test or something i can perform to see if the ball joint is really bad? There is absolutely no shaking or anything while I drive. The only thing I have to go on is this guy's word.

Also, if I were to change the lower control arm myself would I need to have the care aligned?