Story with Rav Safra — halacha l'maseh?

Question

The following story is brought down in Rashi in Makkos Daf 24a (Found in Sha'iltas D'Rav Ahai Gaon)

והכי הוה עובדא דרב ספרא היה לו חפץ אחד למכור ובא אדם אחד לפניו בשעה שהיה קורא ק"ש ואמר לו תן לי החפץ בכך וכך דמים ולא ענהו מפני שהיה קורא ק"ש כסבור זה שלא היה רוצה ליתנו בדמים הללו והוסיף אמר תנהו לי בכך יותר לאחר שסיים ק"ש אמר לו טול החפץ בדמים שאמרת בראשונה שבאותן דמים היה דעתי ליתנם לך

The story goes that someone came to Rav Safra when he was saying Krias Shema wanting to buy something from him. He offered to buy it for a certain amount of money and Rav Safra didn't answer (since he was in the middle of Krias Shema) the person thought then that he wanted more money for it so he offered to buy it at a higher price. When Rav Safra finished Krias Shema he told the person to buy it at the price he said first since that is what I had in mind to sell it to you for.

This story (as far as I know) is not brought down anywhere in Sifrei Halacha or Poskim. However, my question is, is it? Should a person be nohag (behave) this way? Must a person be nohag this way if such a situation were to happen? Or perhaps it is only a "middas chassidus" (pious attribute) for those with "more" Yiras Shamayim (fear of heaven). I'm looking for any sources in the realm of halacha that speak about this sort of situation and how one should be nohag and if it's "m'ikar hadin" (required according to law) or only middos chassidus (or the like.)

Answer 1

Rabbi Moshe Feinstein actually cites this story in a responsum (CM 1:58) regarding joining a labor union. He says that a non-oath commitment made to a union is of very strong religious value; any "G-d fearing person", even if he's not "pious", should make good on his verbal commitments. If Rav Safra made good on his mental commitments, certainly we should make good on our verbal ones.

My impression, though, is that a case actually like Rav Safra's is considered a measure of great piety and is not demanded of an average person. Ask your rabbi if being like Rav Safra is right for you.

As further proof, there's a discussion in Shulchan Aruch (Choshen Mishpat 204:17) of mechusrei amanah (breach of faith); if someone said "I'll buy a hundred widgets from you at fair market value", to renege on that commitment is ethically shameful (though technically legal). There were opinions that if the market value of widgets changes it is completely ethical to go back on the commitment; while we don't rule that way, no one there seems to mention Rav Safra, to the best of my knowledge (other than the above responsum from Rabbi Feinstein).