Is Commission on sale of second-hand goods  included/exluded in National Income

Yes,

Commission on sale of second-hand goods will be included in the national income as it is the income of a middleman for his productive services to various parties.

Middleman provides its services in this whole transaction for sale make happen. He arranges the meetings of the various parties. It helps in negotiation.

It adds to the flow of goods and services in the economy.

Thus, it is included in the National Income of a country.