In The Crucible, how do John Proctor and Mary Warren establish their credibility?

I think that both John Proctor and Mary Warren establish
their respective positions of credibility in different ways.  Mary establishes her
credibility with the people on the "jury" in a contingent manner.  She demonstrates
anxiety and panic in court that feed the public's belief that evil lurks in the town and
that the work of the devil is at hand.  The fact that Mary is a servant, one of the
people, and represents the "common person."  This is what gives her credibility with the
townspeople for she is one of them.  However, it is this very validation that represents
an actual demerit of credibility.  Mary only serves to confirm the emotional contagion
and public hysteria present.  Her credibility is one of contingency.   On the other
hand, Proctor establishes his credibility in a transcendent manner. He stands up for a
transcendental quality that defies the contingency of the time period.  His credibility
is one that resonates with the audience, and not the setting.  When Proctor is sent to
death, rejected by the townspeople, his credibility is actually higher because he
himself appeals to a higher sense of the good.  It is in this depiction that Miller is
suggesting that what is contingent might not represent what should be and what should be
might not be what is.