Answer:
Only John's commission will be counted in the U.S. GDP.
Explanation:
The gross domestic product includes the market value of all final and legal goods and services produced during a year within a country.
The sale of used goods are not included in the GDP since they are not new, but any sales commission generated by that sale will be included in the GDP. All legal services (as long as John pays taxes) are included in the GDP, and John's work as a salesperson is a service.