Sanhedrin 3A

שנאמר: ״משפט אחד יהיה לכם״. ומה טעם אמרו דיני ממונות לא בעינן דרישה וחקירה? כדי שלא תנעול דלת בפני לווין.

The source for this is as it is stated: “You should have one manner of law” (Leviticus 24:22), from which it is derived that all judges must judge in the same manner. And since with regard to cases of capital law it is stated: “And you should inquire and investigate, and ask diligently” (Deuteronomy 13:15), the same should apply to cases of monetary law. And what is the reason that the rabbis said that in cases of monetary law we do not require inquiry and interrogation of witnesses? The Talmud answers: The rabbis established this exemption so as not to lock the door in the face of potential borrowers. If inquiry and interrogation of the witnesses would be required in order to have the court rule that the lender can collect payment of a loan, lenders would be deterred by the difficulty of proving the matter and might cease to lend money to the poor. For the same reason, the rabbis also waived the need for expert judges in these cases.

אלא מעתה, טעו ⁠– לא ישלמו?! כל שכן אתה נועל דלת בפני לווין!

The Talmud asks: If that is so, then if these laymen err they should not be liable to pay compensation to the party unfairly wronged by their judgment, just as expert judges are not liable. The Talmud responds: If this is the halakha, you are all the more so locking the door in the face of potential borrowers; wealthy people will not want to lend money, as they will fear that a court of laymen will judge the case incorrectly.