What should we believe?

Elements that (should) contribute to a believability.

1. Mechanism: I don't believe that astrological sign can affect personality because I cannot think of any possible mechanism. On the other hand I have no trouble with the idea that iboprufen might reduce muscle pain because it is an anti-inflammatory.
2. Independent confirmation: If multiple studies come to the same conclusion this should add a lot to believability unless there is reason to believe that the results of some studies influenced the results of the others.
3. Principle of disinterest or counter-interest: There are many instances where the reporter of some information has an interest in pushing a particular view. Other things equal, we should put less weight on those reports than those provided by neutrals or those who an interest in the contrary position.
4. Understanding the opposition: When two beliefs are widespread, if you undertand (a) why it is that intelligent people can hold the opposing view and (b) how they made their mistake (which error of fact or deduction is at fault?), then you can be more confident in your own belief.