I always tell people to the eye test.
Is it in the fridge or on the shelf?
Real Kombucha needs to be in the fridge beause it's packed with live culture.
Wha's the ingredient list?
There shouldn't be too many, and they should all be natural.
And always make sure that it's unpasurised. If it's not, then the chances are a lot of the live culture has been killed to make it shelf stable.