The judges do have two options. One is to kill Nephi, but the other is to have Nephi discredit himself. If Nephi had accepted the goods offered, he would have violated his religious principles, which were well known. By accepting, Nephi would have negated his position of righteousness, and his prophecy would be null and void in the minds of the people because of his dismissal of his principles. Of course there was no fear that this would happen, and it is quite probable that the judges understood that they would not be able to deal with Nephi so easily.