In "The Odyssey," what are examples that discuss the unfair and arbitrary nature of divine justice. How and why are these examples unfair?...

Your biggest example comes from Calypso in book five of the Odyssey.  When Hermes come to inform her that the gods have ordered her to release Odysseus, she makes a long an impassioned plea about the unfair nature of the justice the gods mete out.  She accuses Zeus of sexism, saying that the male gods take human lovers all the time, but when goddess take mortal lovers, the way Dawn took Orion or Demeter slept with Iasion, the gods immediately grew angry.  She definitely feels like the gods do not have justice in mind but instead arbitrarily enforce whichever rules benefit themselves the most.