2) It is difficult to clarify this point, mainly because you need to find evidence to prove whether the office has effective authorization to use T/T payment method for accounting. You should consider this point clearly and make it clear before signing the contract.
3) Agent C has no certification obligation, so it is difficult for you to ask C to bear the responsibility for work-related injuries on the grounds of inferiority. You can ask Company B to bear the liability for breach of contract by fax.