If I have a freind who is not religious but raised modern orthodox can I stay and eat by him on Shabbos? Can I assume food is kosher? they keep shabbos and yom tov etc.
If he keeps Shabbos, he’s clearly not entirely irreligious. The question of relying on him for kashrus depends on whether or not he keeps kosher for himself. If he does not keep kosher for himself, he can’t be relied on (chashud le’oso davar). However, if he keeps kosher for himself, and assures you that everything is kosher, then he can be relied on, even if he is not particular in some mitzvos.