If you're a sucker, that is.
Actually, that's not entirely fair. All of us are potential suckers when it comes to things we don't know much about. Your Libertarian Car Guy, for instance, knows cars but knows next-to-nothing about computers. So, he is vulnerable to being sold a bag of bull by a computer fixer.
Similarly as regards those who don't know much about cars, especially as regards their workings. Such people can be told all kinds of bull about their cars – and it can sound believable as well as alarming.
Show the sucker a dirty engine and tell him those leaky gaskets ought to be replaced – at $300 a pop. Imply that if they aren't replaced, something really bad might happen. Do not tell the sucker that, as a car is driven, the engine will inevitably get dirty and minor oil seepage around valve/cam cover gaskets is inevitable, normal and harmless. Never explain the difference between nothing-to-worry-about seepage – and a genuinely serious pressurized leak.