The problem with the story that "X said he was shown something amazing by Y" without any physical proof is:
1. X can be making it up. Even if there's no obvious benefit to him, he's getting attention. For many people, that's enough.
2. X could be truthful, but Y made it up. For the same reasons as in 1, but also because many people love the thrill of the hoax.
My father used to tell the most marvellous stories at the drop of a hat. When I reached my teens, I started to call him on those that didn't make sense. "But they're *good* stories," he'd say in his own defense. "Didn't you enjoy them?" He had no intention of truly mislead, just a yen to entertain. He figured that eventually, as I did, sensible listeners would realize they were just tall tales for fun.