re: Do you think it is fair that Chinese automakers can use Mexico to ship cars tax free?

China isn't using Mexico to ship cars. They will assemble cars in Mexico using NAFTA rules to qualify for reduced or duty free tariffs. Other foreign auto manufacturers including VW assemble cars in Mexico that are sold in North American market.
Why shouldn't China be unable to play by the same rules as VW and others?
It will be blood bath after China imposes tariffs and other restrictions on rare earth products. Trump was playing politics with auto workers for their votes.