Chabad.org writes: (edited for the question)
Those who dwell outside the Land of Israel are impacted by the agricultural laws of Shemitah:
Shemitah produce may not be exported out of Israel. However, it is possible to buy "kosher" Israeli produce outside of Israel. For example, if it was grown outside the areas in Israel which are subject to the laws of Shemitah, or if it was grown via the heter mechirah.
Produce which is exported from Israel may only be eaten if it bears reliable rabbinical certification, attesting that it was grown in compliance with the rules of Shemitah.
I have been told that sometimes the label for the origin of produce may relate to where it was packed rather than where it was grown. There is therefore a danger of buying produce from Israel produced during shmittah and in addition not knowing that it was Israeli or shmittah produce.
Is there any Rabbinic discussion about how to avoid problems with buying shmittah produce outside of Israel? What about a shop that on principle does not stock produce from Israel?