Several Etrogim are commonly sold on the market that we can identify with certainty as genuine, authentic Etrogim, and not the product of grafting. One such Etrog is known as the "Hazon Ish Etrog." The Hazon Ish (Rav Yeshaya Karelitz, 1878-1953) planted an Etrog tree and would use those Etrogim for the Misva. It can be presumed that if the Hazon Ish used the fruit of this tree for the Misva, this tree was authentic and not from a grafted plant. Therefore, Rav Michel Yehuda Lefkowitz (1913-2011), a student of the Hazon Ish, took a seed from a fruit of this tree and planted it outside his home. The Etrogim from this tree were regarded as definitively authentic, as they were the products of the Hazon Ish’s Etrog tree. Subsequently, orchards of Etrogim were planted with the seeds of these fruits. Etrogim from these orchards are known as "Hazon Ish Etrogim" and are considered special due to their distinguished "ancestry" which allows us to be certain that they are authentic.
The same can be said about Yemenite Etrogim. When the Jews of Yemen emigrated to Eretz Yisrael in the 1950s, they took Etrogim with them and planted them in Eretz Yisrael. The Yemenite Jews have a tradition confirming the authenticity of their Etrogim, and so Yemenite Etrogim are likewise considered special because of their definitive authentic status. Many Halachic authorities, including Hacham Ovadia Yosef, Hacham Bension Abba Shaul (Israel, 1923-1998) and the Brisker Rav (Rav Yitzhak Zev Soloveitchik, 1886-1959), praised these Etrogim because of their special status. Hacham Ovadia Yosef also praised Moroccan Etrogim, which were likewise known to be authentic, and which were used throughout the generations by many great Rabbis. Another type of Etrog which is known for its authenticity is the Yanover Etrogim, which come from Italy.
Additionally, special preference should be given to the Etrogim of Eretz Yisrael. Rav Yechiel Michel Epstein (Nevarduk, 1829-1908), in his Aruch Ha’shulhan (Orah Haim 648), elaborates on the importance of using an Etrog grown in Eretz Yisrael when such an Etrog is available. He writes that it would be a grave affront to our land if one has the option of using an Etrog from Eretz Yisrael but chooses instead to use an Etrog grown outside the land. This point is made by many other Halachic authorities, as well.
It must be emphasized that the special status of these groups of Etrogim is due solely to the fact that their authenticity can be assured. This certainly does not mean that every Hazon Ish Etrog or Yemenite Etrog is valid for use. There are many factors involved in determining the status of an Etrog, and thus regardless of which type of Etrog one purchases, it is advisable to show it to a competent Rabbi to confirm its validity. Furthermore, one should ensure to purchase his Etrog from a reliable source. Today, Arba Minim stands are set up like newspaper stands, and the people selling the Arba Minim are not experts or necessarily reliable. Just as one would not purchase jewels from some youngster selling them on the street, similarly, one should not purchase an Etrog – a precious commodity no less valuable than jewels – from just anyone who happens to be selling them.