Back in the day, I would look for Doppelgängers when traveling to big cities (like, NYC) by looking for them in the phone book. No one in NYC had my name at the time. Now with Google I have found a couple of them in other countries. However, I would not expect Marriott to let them use my Bonvoy account if all they could provide was my first and last name. And I would not expect a Marriott hotel to look up existing members and tie customer reservations to those accounts simply based on a name match when they get a list of guests for a group booking. It’s not identity theft, of course, but really bad business practice if they do this routinely.