Commentary for Avodah Zarah 78:6

The baraita here refers to buying food from Jews in Syria, the area which lies to the north of Israel. This is an area that rabbis usually consider “semi-observant.” According to the baraita, merchants there are not so careful not to sell to Jews products that were meant for non-Jews. All of these items may be forbidden to Jews. However, he may buy them from a reliable person. He may also eat with Jews there because the Jews there do not themselves eat these foods. Furthermore if a Jew sends him some food as a gift he will send from the food he himself is eating. We can assume that this food is kosher.