If all you are doing is casting reasonable doubt, that's fine. The logical fallacy arises when you point to the source of a proposition and declare that mouth t

If all you are doing is casting reasonable doubt, that's fine. The logical fallacy arises when you point to the source of a proposition and declare that mouth that spoke it makes it false by nature. There's a big difference between "This pro-coffee study was funded by Big Coffee, so I'm skeptical and would like further studies and independent verification" and "This pro-coffee study was funded by Big Coffee, therefore the conclusion is false and coffee actually isn't good for you." Even if Big Coffee funded this report and benefited from its conclusions, the conclusions may very well still be valid; it would be a fallacy to reject this possibility outright.