"Last Favor" is a science fiction short story written by Harry Turtledove. It was originally published in Analog Magazine in mid-December, 1987 and reprinted in the Turtledove collection Departures in 1993.
Jerome Carver is a merchant-trader on the spaceship Enrico Dandolo on a mission to the planet Ephar. The centauroid natives of Ephar were of two races, the dominant blueskins and the brutally oppressed greenskins. Earth's policy was not to intervene unless requested and yet the greenskins adamantly refused to make that request. Carver, who has made previous trips to the planet, decides to find a way to intervene.