Recognize the situation when both the parties in a barter economy have agree to sell and buy each other's commodities ? What is it called ?

Dear Student,

This is known as a double coincidence of wants.  Double coincidence of wants refers to a situation in a barter system where the goods or services offered by a seller are exactly the same as that required by a buyer and vice versa. The barter system of economy in which money is not prevalent as a medium of a transaction depends upon this situation for a successful transaction.

Regards