Marriott don't really care too much about how a booking is made, it's the hotel that is ultimately responsible for your conduct on the property and for getting paid: if you make a fraudulent reservation using a stolen account then it is the hotel who will be on the hook for any costs. Due to the rise in fraud (especially from stolen accounts) hotels are becoming more and more strict, nowadays it's all but impossible to check in without being the named guest on a points booking (and even on a cash booking in some cases).
The point above is exactly the reason why hotels must follow the rules and ensure the name of the person on the booking matches the person checking in - ultimately they are on the hook for fraud (and not Marriott). However given the fact Marriott gave incorrect advice twice I believe they should at least refund the points used for the reservation.