As to how to know what to believe: you need a certain degree of familiarity with how things work in the realm of discourse. You can readily recognize patterns of data which seem consistent with that familiarity. If you're a farmer and you go to sea for the first time, everything may seem to be something amiss, with t he creaking and rolling and pitching. Conversely, a seasoned deckie knows what to expect, and will know what really is an anomaly when one appears.

With a background off familiarity, you also know how to recognize distortions such as altered sequences, falsified data, exaggerations about time, and the most popular form of BS, distortions about what is important and what is not in a given field. There is a long list of typical patterns of falsification which you could draw up, ways in which people twist information to serve their own purposes, with little respect for the truth. But ther eis also such a thing as the truth, or at least a sufficient degree thereof.

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