It is a frustrating process; however can save money. I am a Hilton Diamond member. I have had the best experience and most success when I call during US business hours and ensure that I actually have reached the Diamond desk...I book with the Hilton representative so that I don't risk the eventual denial when you submit the web form after making the reservation...almost all of my "Best Price" matches have been honored without too much difficulty.

I booked the Doubletree in Lisbon, Portugal yesterday. The Hilton agent simply compared the hotels.com price for a king room to the Hilton.com rate and honored the lower rate, less the 25%. Probably the easiest time I've had.