May one sell or purchase a Shemita Esrog?
In the Sukkos of the eighth year the Esrog of Jewish owned fields in Eretz Yisrael is treated as Kedushas Sheviis and hence may only be purchased through Otzer Beis Din, or Havlah as explained next.
Otzer Beis Din: A Halachilcly reliable Beis Din takes authority over the distribution of the fields Esrogim and collects a minimal fee for the Esrog in order to cover the expenses of the distribution.
Havlaah: One may sell before Sukkos a Shemitah Esrog that is not Otzer Beis Din, if he does so in Havlaah. This means that one includes the sale of Shemitah produce within the sale of other products that are not from Shemitah. Thus, for example one may sell before Sukkos a Shemitah Esrog together with a bag of lemons. One may charge an over the market price for the bag of lemons, due to the included Esrog, if the Esrog is not given a specific price and is simply part of the package. The money received for this payment does not have Kedushas Sheviis. [However there are some Poskim that are stringent and prohibit selling even in Havlah, and Havlah in their opinion only helps in the fact that it does not give the money a status of Kedushas Sheviis. Practically the custom is to be lenient.]
May one import Israeli Esrogim of Kedushas Sheviis to the Diaspora for Sukkos?
Some Poskim rule it is permitted to do so even initially, on condition that the Esrogim are sold Behavlaah. Other Poskim rule it is initially forbidden to do so. Some Poskim rule it is permitted to do so in a situation that the city will not have any Esrogim available if they are not sent. According to all, even if an Esrog was taken out of Eretz Yisrael in a forbidden manner, it remains Kosher and can be used for the Mitzvah.
 Minchas Yerushalayim 7/36; Shemitah Kehilchasa 4/4
 See Piskeiy Teshuvos 649/7; Beis Yitzchak Y.D. 2/121; Beis Ridbaz 5/18
 Mishnas Yosef 2/24-28; Tzitz Hakodesh 1/15; Piskeiy Teshuvos ibid; See Beis Ridbaz ibid
 See Beis Ribaz ibid as Esrogim don’t require Biur.
 See Mishnas Yosef 2/24-28
 Beis Ridbaz 5/18; Igros Moshe 1/186
 Chelkas Yaakov Y.D. 185; Chazon Ish Sheviis 10/6; 13/4; See Beis Yitchak ibid
 Chazon Ish
 Chazon Ish ibid; Igros Moshe ibid