Over-the-counter transactions are not registered at the product supply and marketing meeting, but are concluded privately at a price higher or lower than the price stipulated by the supply and marketing meeting or with other conditions (such as matching inferior goods and bartering things). Over-the-counter transactions often occur when the supply of goods is in short supply or some regulations at the supply and marketing meeting are unreasonable. It is easy to create unhealthy trends and even provide opportunities for speculators. To put an end to over-the-counter transactions, fundamentally speaking, it is necessary to establish and maintain the coordination of the proportion of supply and demand of commodities. On the other hand, the advantage of OTC trading is that buyers and sellers can negotiate special trading conditions without following the standard contract of centralized market, such as buying and selling foreign exchange forwards for more than one year (centralized market does not provide foreign exchange forwards). However, the disadvantage of OTC trading is that market information is not open, there is no stock exchange to guarantee performance, and the risk of due performance is high.