IIRC, Homer's epics were centuries after the Trojan War. It would have been difficult, even in that era, to fake this.
Homer was simply the first person to write them down. They had been passed down through the oral tradition since the Trojan War. Prior to Homer they would have been as familiar in the Greek world via story tellers as Hollywood is to us.
There are a lot of details in Homer that seem to be authentic Bronze Age features (not only with weapons, armor, the walls and location of Troy, etc. but also details about Odysseus' ship and such) that had changed by the time of Homer, suggesting the stories have at least a Bronze Age core to them. I'm not sure if archaeology will ever answer questions such as wether the Trojan War was really started over Helen and ended with a wooden horse, though.