Even supplier provide all correct, Customs still inspect the shipments randomly.

And in some special time like before national day or Chinese new year holiday season,the inspection could be more strict.

If ever inspected, the whole container or air shipment will be hold and waiting for further release.

Consequently, inspection fee and storage fee will be incurred. Those costs will be charged as per the Customs receipt.

Who pay this ?

It depends on the Incoterms.

If FOB, your supplier will pay; If EXW, then it will be on your account.