A coworker of mine started falling down the YouTube conspiracy rabbit hole. He said something about the moon landing maybe being a hoax. I told him that when I was in college I used the big telescope to look at the moon landing site, so I knew for sure it was real. After that, he believed in the moon landing.
Now of course I was lying about seeing the moon landing site. Terrestrial telescopes can't see the landing site. I convinced my friend to believe the truth by countering a lie from a stranger with a lie from someone he trusts.