Dignas, Beate, and Kai Trampedach, eds. 2008. Practitioners of the Divine: Greek Priests and Religious Figures from Homer to Heliodorus. Hellenic Studies Series 30. Washington, DC: Center for Hellenic Studies. http://nrs.harvard.edu/urn-3:hul.ebook:CHS_DignasB_and_TrampedachK_eds.Practitioners_of_the_Divine.2008.
10. Authority Disputed: The Seer in Homeric Epic*
1. Calchas at Troy (Iliad I 53–117)
Before Calchas addresses the question of the cause of the plague, however, he requests a promise of protection from Achilles, because he fears that some day he may fall victim to the vengeance of someone powerful. After Achilles has promised him protection, Calchas says what the audience already knows: the wrath of Apollo, manifested in the plague, was provoked by the contempt shown towards Apollo’s priest at Chryse, whose daughter was abducted by Agamemnon, who refused to surrender her even when he was offered a generous ransom. The conciliation of the god requires the unconditional return of the maiden to her father, and a hecatomb in the sanctuary of Chryse. The reaction of Agamemnon fulfills expectations, and is directed first against Calchas:
In spite of this insult, Agamemnon agrees and declares himself willing to return the maiden in the interests of the army, though not without justifying himself in a rather offensive manner, and then demanding a suitable compensation for the loss of his honor gift, which provokes the wrath of Achilles. The doom of the Iliad takes its course.
2. Calchas at Aulis (Iliad II 299–353)
Odysseus himself is convinced that the prophecies are true, as he emphasizes again at the end of his speech (II 330), but obviously he cannot take this for granted. The enthusiasm with which the Achaeans react to his speech (II 333–335) speaks for the rhetorical skill of Odysseus. 
3. Helenus (Iliad VI 73–102; VII 44–53)
The fate of Hector is not, however, discussed in the conversation between Athena and Apollo (VII 23–42).  In any case, the statement op’ akousa theōn (VII 53) seems to imply that he literally heard what the gods said to one another.
In contrast to Calchas, the poet does not say that Helenus owes his ability to a god. Rather, the leading mantic specialist on the Trojan side is shown to have an instinctive ear, which proves equally well his own closeness to the gods.
4. Polydamas (Iliad XII 195–258)
If Polydamas can play the seer without actually being one, then one quickly gains the impression that in general, no special or secret knowledge is necessary in order to interpret Homeric signs from the gods.  At the same time, perhaps Polydamas also fails because his advice lacks the authority of a specialist.
And (c) he attacks the integrity of the interpreter by suggesting that Polydamas’ real motivation is cowardice. This assertion subsequently finds expression in his threatening Polydamas with death.
5. Halitherses (Odyssey ii 1–259)
6. Theoclymenus (Odyssey xv 222–286, 508–546)
7. Conclusions: The Seer in Homer—and Beyond
The way in which seers observe and read and decipher such signs in reference to the situation demonstrates the competence of the seer, which, however, should not be regarded as exclusively his own. The art of the interpretation derives from a practical intelligence and is an individual power, not (as again, for example, in Mesopotamia and Etruria) a privilege of a particular group. Besides seers, other prominent figures appear as interpreters of signs; and because of their social position, these others are in a better position to impose their views.  We find the same constellation in later sources, in which the first recipients and interpreters of unsolicited signs are more often military commanders and politicians than seers. Yet if technical expertise is not conspicuously important, and if interpretative competence is not invested exclusively in them, then on what basis do seers acquire their reputation? I agree with Michael Flower’s view that membership of certain families and, above all, a personal and reliable charisma proven by success, are deciding factors.