So being that I've never done this, is is pretty obvious if the wax has been removed after the wash?

 

First sign will be the water sheeting on the paint instead of beading. You can also take a cotton ball and soak it with alcohol and rub on a test spot. Once the alcohol has dried you should feel no difference between the test spot and the surrounding paint as far as smoothness or slickness - squeaky clean.
Now you're ready for clay.