Menachem from Bnei Brak asks: 

We follow the ruling of the Chazon Ish, z’tl, that produce grown by non-Jews on
non-Jewish owned land in Eretz Yisroel does have kedushas shvi’is.
How do I acquire such produce in Yerushalayim, where the prevalent custom is
that non-Jewish produce has no sanctity?

Let me first explain your question. One may not trade in produce which has kedushas
. The custom in Jerusalem is to treat non-Jewish produce as having
no sanctity. Accordingly, it may be sold in the usual way. However, in Bnei Brak
such produce is considered as having kedushas shvi’is. It may
therefore not be sold in the usual way. Since the storeowner is permitted to
purchase this produce from the non-Jew, the accepted method of acquisition is
that the customer appoints him as his agent to buy from the non-Jew. However, a
store following Minhag Yerushalayim (the Jerusalem custom) may not have
this facility available. What options are then open to one who follows the
ruling of the Chazon Ish? Firstly, there are those who are of the opinion that
the prohibition of trading is on the seller, but not on the purchaser. Since the
seller is just following his local custom, one could argue that by purchasing
from him in the usual way one is not causing him to do anything wrong.
Nevertheless, a further method is available (according to many opinions), which
will avoid this problem. This is known as havlo’oh (absorption). It
works as follows. One purchases an item which definitely does not have kedushas
(for example, sixth year produce) together with the non-Jewish
produce. A higher than usual payment is made for this ordinary produce, and the kedushas
non-Jewish produce is given for free. Thus, one has not purchased
the non-Jewish produce which has kedushas shvi’is according to the
custom of one’s hometown.