There are certainly a number of different elements you could look to in the story to support this statement. The most important, though, is the way that after Daniel Webster has cogently argued that Jabez Stone is constitutionally entitled to a trial with a judge and a jury, the Devil selects a variety of pirates and other n'er-do-wells to form the jury, and Judge Hawthorne, the infamous judge of the Salem witch trials to judge the case. Note how they are introduced:
One and all, they came into the room with the fires of hell still upon them, and the stranger named their names and their deeds as they came, till the tale of twelve was told. Yet the stranger had told the truth--they had all played a part in America.
The way in which the judge enters muttering "Hang them all!" in relation to the witch trials likewise strikes "ice into the soul of Jabez Stone." To what extent can he expect to have a "fair" trial with such a jury and with such an unyielding and definant judge, who is famed for hanging so many innocents? Clearly, the notion of Jabez Stone receiving a "fair" trial at this stage is clearly laughable.