Judging

(i) Hidden

Chinese martial arts were usually a family or village system used for self defence. Sharing with outsiders was not encouraged.
Tai chi was designed specifically to hide the applications and skills within an innocuous-seeming range of forms, drills and exercises.


(ii) Feeling

Tai chi skill can only be determined by how it feels. Martial arts are hands-on.
If your tai chi is generating the effect using the correct means, then this will be physically evident when you partner up with somebody else.
The very definition of 'jing' is somebody else's experience of your tai chi.


(iii) The Tai Chi Classics

Tai chi must adhere to the tai chi principles. Given the internal nature of tai chi, many of these cannot be gauged through observation.


(iv) Aesthetics

The danger with aesthetic concerns is that the context is askew.
People look for particular alignment considerations based on how nice they look instead of determining how they add to your ability to generate jing.
Tai chi is a living, breathing martial art in the hands of the right person. Arbitrary aesthetics will rob the practice of any viable self defence application.