I have been a loyal marriott member for over 10 years. I was giving my rewards number to hotels (Last 4 stays). When I check in while on another trip and ask to add my rewards, clerk informed me that if I made reservations thru expedia, kayak or any third party booking, they do not honor and will not give reward points. I was shocked to find this out. When I called customer service, they informed me its embedded with in the terms and conditions which I agreedto 10 years ago. Since my company books thru 3 party to save $ and have a one stop booking for air, hotel, car., I will ask them to remove marriott as a preferred hotel from my profile. Sad to find out I am no longer a loyal marriott customer, I feel I was decieved and only when I clerk mentioned did I find out. This deception is not called out on the web site marriott.com or on your account. Said that a hotel I respected is in the business of burying this very important detail. Link were its located under the terms and conditions = https://www.marriott.com/rewards/terms/earning.mi, section 9-rooms booked through third party online retailers, such as expedia.com, orbitz.com, travelocity.com, and hotels.com, as well as operators of opaque booking channels such as priceline and hotwire are not eligible for points or elite night credit.
I hope this helped inform other marriott reward members.