From inter- +‎ sale.

intersale (uncountable)

1. The sale of goods or services to each other by multiple parties.
   • 1932, United States. Dept. of the Interior, Annual Report of the Department of the Interior, page 55:

     The electric connection with the Utah Power & Light Co. for the intersale of power, which was completed July 18, 1931, has proved highly satisfactory, providing complete breakdown service and an outlet for surplus power generated.