Marriott Rewards has a Best Rate Guarantee program called Look-No-Further that promises to match lower rates found on third party sites and to give an additional 25% discount.
Marriott has tweaked the guarantee a few times and made it easier get approved claims for stays outside of North America most recently.
You can access Marriott Rewards Best Rate Guarantee here.
Here are the changes as of September 1, 2016:
1. Delta Hotels
All Delta hotels are now participating to the Look-No-Further program. Previously they were not participating.
2. Submission Deadline
Previously, you had to submit the claim within 24 hours of making the reservation or by 11:59PM local time on the day of arrival. The claim deadline has now been changed to 10PM local time for claims made on the check in date.
Good that Delta Hotels are now part of the Best Rate Guarantee program. Quite often you cannot book hotels past midnight local time. It makes sense for Marriott Rewards move the submission deadline to 10PM.
I did quite a few claims in May (and have been thinking of writing about them) and was surprised how fast claims for same day arrival were processed (usually within few hours).