The best way to assess the credibility of a source is:
C from determining whether or not it seems to be fair and unbiased.
Assessing the objectivity and fairness of a source helps ensure that the information is reliable and not skewed by personal biases or agendas. Other options may touch on factors that play a role in credibility, but evaluating fairness and lack of bias is crucial for determining the trustworthiness of the information.