I understand that for some tasks or jobs (particularly those relating to kashrut), Judaism ritually requires more than the criteria of matrilineal descent to qualify as a Jew. E.g., as I understand it, strict observance of shabat for the ones raising the dairy is required for some levels of chlov yisroel.
Given that, what constitutes a gentile for the purpose of selling chametz?
Is it allowed to sell the chametz to a cousin who is known to be of Jewish descent but does not observe halakhically at all, and will not even attend a Seder?