It is not positive sum, in competitive market it is basically exchanging services, and each party has to agree on mutual value of services being exchanged otherwise no trade.
Accountant values his labor as 100/hr and plumber values his services as 100/hr and they simply exchanche services.
Accountant values his labor as 100/hr and plumber values his services as 100/hr and they simply exchanche services.
How is it positive sum?