Credibility plays an enormous role on historical research. People who research history are often working with information that other people have researched first. They use this information in order to reach their own conclusions. Therefore, they need to be able to trust that the information was obtained in a careful, systematic and unbiased way.
One of the ways in which you can ensure this is by looking at the credibility of the person who conducted the research. If the person has conducted other research, and is well-accepted in the scientific community, then it is more likely that his research is trustworthy.
One of the ways in which the researcher can incorporate this information into his own is by using integrated sources throughout his text. This will ensure that readers are aware of the quality and the origin of the information the researcher is presenting.