It's important to be aware that The Iliad concerns the Olympian gods almost as much as it does the mortals fighting the Trojan War: in that respect the action in the epic is actually divided into two separate but interrelated spheres; mortal and divine. I would say, on a question like this, some of the epic's most striking displays of trickery and manipulation are actually displayed by the Olympians, as they attempt to manipulate the course of the war.
For example, consider the beginning of Book Two, when Zeus sends Agamemnon a dream. This dream is essentially a false omen of victory. As The Iliad states:
With these words the dream went off, leaving Agamemnon with a false picture of the future in his mind. He imagined he would capture Priam's town that very day, the fool. He little knew what Zeus intended, nor all the sufferings and sorrows he had in store for both sides in the heat of battle. (The Iliad (Penguin Classics Ed.) trans. E. V. Rieu, revised and updated by Peter Jones and D. C. H. Rieu, p. 22)
Prophesies and omens are key themes across much of Ancient Greek mythology, and they are accordingly given a great deal of weight. In this scene, Zeus is manipulating the idea of prophesy in order to deceive. Remember, Zeus's sympathies lie with the Trojans...
A second example can be found in Book Four, carried out by Athena (perhaps the most cunning of all the gods). By this point in the poem, Menelaus and Paris have had their duel (with Aphrodite spiriting Paris away before he could be killed), and the two sides are currently in a truce. Violently opposed to Troy, Athena wishes for the Trojans to break the truce so that the fighting could restart (with all dishonor for oath-breaking falling upon them rather than the Greeks). Thus, she intercedes personally, disguising herself and entering the Trojan camp, convincing one of the Trojans, Pandarus, to kill Menelaus with his bow (even as she manipulates his attack to ensure Menelaus's survival).
As one final example, I would point towards Book Fourteen. Unlike the other two examples, this isn't a case of the gods manipulating mortals, but rather of the gods manipulating one another. Remember, the gods themselves are divided over the Trojan War, with Zeus, the king of the gods, sympathetic to Troy. Hera, meanwhile, is aligned with the Greeks. Thus, in this book she seduces her husband in order to lure him to sleep, so that Poseidon could assist the Greeks free of Zeus's intervention.