Originally Posted by bgriff

You may have already considered, but one thing to check -- does the cash room availability still show up if you search signed out in an incognito window? Marriott.com appears to show rooms available under the elite room availability guarantee when you search online if signed in, so there can be cases where a hotel is genuinely sold out and therefore it makes sense that no points rooms are available, but when signed in they'll still show you a cash rate under the availability guarantee. (And if you booked the cash rate, and nobody cancelled or no-showed between now and the date of the stay, presumably they would end up walking someone from the hotel during your stay.)