One year, there was a severe shortage of unblemished Esrogim. A Chosid of the Heilige Rebbi Israel of Hussiatin ztz"l, a prominent merchant who traditionally provided the Rebbe with his finest Esrog, could find no completely clean specimen. He sent the finest one available, which bore a visible spot.
The Rebbe's attendant, Reb Kalman Shaul, realized this was the best specimen available and placed it into the Rebbe's Esrog box. On the first day of Succos, the merchant walked an hour from Meah Shearim to Kiryat Moshe to pray with the Rebbe. As he arrived, Reb Kalman Shaul greeted him joyfully, saying, "Come, I want to show you the Esrog you provided!" Fearing something had gone wrong with the Esrog, the merchant inspected it closely, turning it over to look for the spot-only to find it completely clean and flawless! The merchant was dumbfounded. The attendant explained: "After the Rebbe recited the blessing over the Esrog, I picked it up to bring it out for the congregation, and I noticed the spot had completely vanished."
A similar story is told regarding his father, the Holy Rabbi Mordechai Shraga of Hussiatin ztz"l, who used to inspect Esrogim thoroughly before use. Eventually, he ceased inspecting them, explaining that since every Esrog he used became pure and beautiful after he recited the blessing, there was no need to search. Other great tzaddikim were known to simply reach into a box of Esrogim and draw one out, trusting that whichever landed in their hand was destined for them, and it always proved beautiful.