Christians are vetted by getting in touch with bishops, priests and family.
I will say, some of my closest friends over the years have been Syrian and Lebanese Christians - all good, Godly folk. But, that was then, this is now....
but what if ISIS sets up posers to fill all of the above roles? Its very common in debtor fraud. There are crime rings that go around buying vehicles with false identities that list mail drop or faux addresses that look real on paper but are vacant lots. The "buyers" also list references that are all fake thatnuse cell phones which answered by other members of the crime ring to pose as whomever they want them to be.
Middle eastern Christians are the best people for vetting middle eastern Christians. They know the quirks and tells of those muslims who will try to pass themselves off as Christian. Many of them still have Christian family in the mideast. The archbishop of Baghdad grew up in the Detroit area.
Middle eastern Christians have been in SE Michigan and NW Ohio for 100 years. Think Danny Thomas, Jamie Farr, and Kasey Kassem.