Authentic tai chi can be found. You just have to look for it. Be patient. Be discerning.
Go to different schools and find out what they are teaching and how they are teaching it.
Be humble. Be quiet and receptive.
A good teacher should be able to illustrate internal power without any difficulty.
Watch for ease, comfort, consideration and softness.
It should look like no effort was required. It should feel to be without force, without conflict.
A good teacher is composed. They are graceful, smooth, unhurried. Never aggressive.
Their self defence skills should be quietly impressive. Effective. Decisive. Final.