A quick way to debunk any conspiracy theory is to look beyond the statement of the conspiracy, and consider the systemic implications of it, that is to say, what would have to be true, in the wider world, to make that conspiracy theory true.
For example, the moon landing conspiracy. There are people who legitimately believe man never walked on the moon. That NASA faked the moon landing, to get one up on Russia in the space race, as a bit of cold war propaganda. Let's follow that line. Russia was ahead for most of the space race. First object in orbit. First living thing in space. First man, first woman in space. First space-walk. First space station. First off-earth rover. That rover was the Lunokhod. If I recall, Russia landed two of them on the moon. If America faked the moon landing, Russia just needed to land a Lunokhod right where America claimed Amstrong and Aldrin landed, and send back pictures of the vast emptiness. If America faked the moon landing, Russia could get away with faking that. What evidence would America have to challenge them? Faking the moon landing is a huge gamble, when your opposition has a device that can transmit images back to earth, and when your opposition might succeed in what you faked, and show you up. Russia was America's biggest military, economic, and ideological rival for decades. Don't you think, at any point up to the late 90s, that Russia would have loved to destabilise America's credibility by proving they'd faked the moon landing?
The logical conclusion of the faked moon landing must be that the people the landing was faked to scare, the whole reason for the space race, would have to be in on it.
Climate science. Apparently there's this global conspiracy of scientists to fake the climate data, and overblow the danger of rising CO2 levels, just so they can get fat off grant money. This one is easy. For this to be true, the fossil fuel industry must be completely powerless against a financial incentive! I mean, how ever would the fossil fuel industry get the money to compete with government-funded research grants?