According to James Avery Smith, a Samuel Parsons of Northampton, Massachusetts, was selling enslaved people as late as 1790, when he sold Wealthy Wheeler (c1785-1871) to Oliver Cowls (Cowles) (1765-1850) of Amherst, Massachusetts. (James Avery Smith, A History of the Black Population of Amherst, Massachusetts, 1728-1870 (Boston: New England Historic Genealogical Society, 1999), pp. 10; 130.
operson_detail.html