when two people each have items the other wants both parties can determine the values of the items and provide the amount that results in an optimal allocation of resources 
for instance if an individual has 20 pounds of rice that they value at 10 they can exchange it with another individual who needs rice and who has something that the individual wants that s valued at 10 a person can also exchange an item for something that the individual does not need because there is a ready market to dispose of that item 