On general terms, I think this would be classified as self employment income. However, it also sounds similar to extra commissions or “spiffs” that auto manufacturers pay to successful salespersons. Although you “earn” it by selling cars and the salesperson is an employee of the dealership, the spiff is considered unearned income and is reported in box 3. I don’t know if the “spiff” treatment is specific to the car industry or not. I need to do some research.
