The so-called "spot warehouse receipt transaction" is actually an illegal futures transaction under the banner of spot, which is an illegal management loophole. Without the approval of the CSRC, all transactions in the form of forward contracts are illegal.
Therefore, I suggest you don't get involved. Although the regulatory forces may not control these illegal transactions for the time being, there will be big problems sooner or later because there are no rules formulated by the state. And once there is a problem, it is the people involved in the transaction who suffer. There is a precedent in Hainan rubber market in this respect.