Your post is an excellent one,WarningSigns:

If they need 10 teachers, they'll hire 15, keep 15 on reserve as pending. They'll hire them, but will not pay any fees for them until they have performed a demonstration class. They will then release 5 of them immediately as "unfit to teach". Then, over the course of the month, any teacher that does not perform 100% (including things like how you get along with management, how much input you give (only when asked), how you present yourself, etc) will be released. By the end of the month, they have 4 teachers left, and they hire another 10 or so and go through the same process.

Please allow me to add that 'they' will most probably be Training Centres.And the discarded teachers 'over the course of the month' will have foolishly come to China with L visas, necessarily making their employment insecure.Such teachers will have to exit the country promptly,as they will have insufficient time to fix up alternative employment before their tourist visas expire.
Unscrupulous Chinese employers are far too prevalent among Training Centres here.If I had my way,I'd have them all shut down!