They also said that the UPPSC has not followed the Allahabad High Court's order of March 30 by which it had directed for re-evaluation of answer sheets of the preliminary examination.
"The sanctity of an examination will be lost if we keep on interfering with the decisions taken by an authority conducting the competitive examination through the power of judicial review," the bench said.
The mains examination, which was earlier postponed, is now scheduled to be held on June 18.
The high court, in its March 30 order, had also said that candidates who were found to have qualified the preliminary examination as a result of re-evaluation would be entitled to appear in the main written exam.
The UPPSC has challenged the high court's order in the top court, which had on May 18 stayed the high court's directive.
During the hearing today, the bench said that courts could use its power of judicial review and direct for corrective measures only when there was a manifest error or a human error, which on the face of it was wrong.
"In writ jurisdiction, we can only see whether the due process of law was followed for arriving at a decision or not, but we cannot go into the decision itself," it said.
Additional Solicitor General Maninder Singh, appearing for the UPPSC, said that the commission had set up two committees of experts, which deliberated on all the 962 objections raised by the candidates after the prelims examination.
"The committees of 26 experts conducted a workshop for two days and examined all the objections after which the final list was declared on January 19, 2018," he said, adding that the examination should not be stalled or cancelled.
Singh said that there were several verdicts of the apex court, which said that decision of an expert committee will be final and the top court should not stall or cancel the mains examination as arrangements have been done for over 16,000 candidates, who have qualified the preliminary examination.
The counsel appearing for some of the students, who had challenged the results of the preliminary examination before the high court, said neither the first answer key declared by the UPPSC in November last year nor the second answer key declared in January were "sacrosanct".
To this, the court said, "The courts can only interfere with the decisions only when there is a human error or a manifest error which on the face of it is wrong."
"In the present case, we have to see as to what extent the court can go otherwise it will be a never ending exercise," it said.
It said that in the present case, there was an in-built process of moderation and all the objections were considered and examined by an expert committee of 26 members.
"The committee spent two days of time and energy to deliberate upon the all the 150 questions that were asked in the preliminary examination and the objections raised after which the results were published along with answer keys on January 19," the court said.
The top court said that the situation would have been different had the moderation exercise was not followed in the present case or there was a palpable error.
"Where there is no such possibility, in our opinion courts should not enter into such arena. Otherwise what purpose did the 26 members expert committee meant to re-examine the answers to the questions served," it said.
The top court said wherever a proper reasoning was involved to reach at a particular answer, the court should not enter into that arena.
The high court in its order on March 30 had refused to direct the commission to hold fresh preliminary examination, but had asked for re-evaluation of answer sheets of all the candidates after deleting one question.
The UPPSC had conducted the examination for 677 posts of upper-subordinate services of the state for which advertisement was issued on February, 2017.
The preliminary examination for 677 posts was conducted in September 2017.