I was just denied a claim against booking.com and the reason given was:
I am unable to approve your claim because, per our terms and conditions, comparing Marriott channel rates to those found during later searches on Marriott channels (including Marriott-affiliated, private label, or property standalone websites) are not eligible for the guarantee (Applicable Rates at the link provided below).
Is the rep claiming that booking.com is a Marriott channel?

The denial also said:
The cancellation policy and rate rules of your reservation were presented at the time of booking. As a reminder, those rules are:
- Advance Purchase rate
- Full room & tax payment due one day after booking
- Non-refundable rate
- Cancellation permitted up to one day after booking

Because of these rate rules, we are unable to modify your reservation to any lower rate now being offered
This makes some more sense to me, but doesn't seem to align with their best rate policies?