Sruli was learning for the year in Israel and buying a lulav and esrog for himself for the first time. His rebbe had given his class a shiur about the arba minim, and Sruli tried to remember all the halachos as he browsed the stands. He found an esrog that seemed okay and was inexpensive. It had a couple of small spots and scratches, but he didn’t think they were a problem.
“I think I’ll take this,” Sruli said to the seller, “but I’d like to consult my rebbe. If it turns out to be a problem, can I return it?”
“If your rebbe says you can’t make a berachah on it, you can return it,” the seller answered.
Sruli took the esrog to his rebbe. “Overall it looks okay, but there’s a small gouge in it,” his rebbe said. “We mentioned that such an esrog is called chaser (missing), and I’m afraid it’s not kosher.”
“So I should return it to the seller?” asked Sruli.
His rebbe thought for a minute. “In a regular year, when the first day of Yom Tov is on a weekday, I would say yes,” he replied. “However, this year the first day of Yom Tov falls on Shabbos, so the halacha may be different. I’d like you to speak with Rabbi Dayan.”
Sruli called Rabbi Dayan, who told him, “As esrog that’s missing even a small amount is considered chaser and invalid for the first day of Yom Tov according to most opinions. However, it’s kosher on Chol HaMoed when the obligation to shake lulav and esrog is rabbinic” [Orach Chayim 648:1; Rema 649:5].
“Outside of Israel, we treat the second day of Yom Tov like the first day regarding most halachos of the arba minim. However, since there is a minority opinion that an esrog with a small gouge is kosher even on the first day, we allow making a berachah on it on the second day, but it isn’t mehudar” [Mishnah Berurah 648:8].
A pasul esrog is a mekach ta’us [defective merchandise] and can be returned to the seller, similar to food that proves to be non-kosher [Choshen Mishpat 232:11-12; Sma 232:28].
Even if for some people the esrog is kosher, if it’s pasul for the buyer, it’s also mekach ta’us. Moreover, if a person is known to be stringent to buy only a mehudar esrog, it’s considered a mekach ta’us for him [see Rema, Choshen Mishpat 233:1].
“However, since chaser doesn’t disqualify an esrog from being able to make a berachah on the second day, and the amount you paid is not reflective of desire to be stringent and only buy a mehudar esrog, you can’t demand a refund.”