Easiest way to know someone never read the Iliad? They refer to events or characters from the Trojan War that weren't in the Iliad.
The sacrifice of Iphigenia was not in the Iliad, in fact taking into account that the name of Iphianassa, one of Agamemnon's three daughters in the Iliad, may simply be an older variant of "Iphigenia" and her being offered as Achilles' wife, would suggest she wasn't sacrificed or spirited away to Tauris but still living in Mycenae.
The death of Achilles and his heel was not in the Iliad. He was not nearly invulnerable, the whole heel thing comes from the Achilleid. In the Iliad, Achilles gets his hand injured by Asteropaios and it is even a plot point that he needed a new set of armour.
For a third and final example, the Trojan Horse was not in the Iliad. It is briefly alluded to in the Odyssey and shown in full in the Aenied, but it is not in the Iliad.
The Iliad does not cover the entire Trojan War. This needs to become more well-known.
