Probably because of my rigid academic training in my youth, I've learned to use multiple sources and test them to see if they are well-documented--preferably by a wide range of original, rather than second-hand, sources. I have especially applied those principles to my current interest, Civil War history. One thing I have learned from this field is that history is not fixed! New original sources are constantly becoming available, as people check their attics and find that the "rubbish" includes letters and other documents from Civil War ancestors. They donate them to universities and museums, which are making a strenuous effort to digitize them so everyone can access them online. For one spectacular example, it's only very recently that the entire collection of U. S. Grant papers has become publicly available--at, of all places, Mississippi State University!