I had a recent experience where I had a two night reservation.
Upon checking, I was informed they had no rooms. After about 5 minutes, the front desk informed me that they had one room (different than what I booked) for one night, but I would have to checkout in the AM. I thought it seemed odd, but I didn't fight it and checked out the next morning. My colleague and I were chatting the next day (we are both Platinum elite) and he informed me about Elite guarantees with Marriott. I thought that was cool so I opened a case with Marriott. case number - 24330568.
Marriott has given me a run around about the guarantee. I was formerly happy with Marriott, but I think I going to shift the bulk of my hotels to Hilton since I am also Diamond elite with them. In case anyone is wondering, the details of the guarantee are here - Marriott Rewards® Elite Benefits Guarantee
The total customer service experience has been awful. Today, I was told that this only applies to reservations booked 48 hours in advance (website doesn't say that). I was told it doesn't apply to silver (I told the person in customer service I was reading the website not that I care cause I am platinum.) She said that she had been trained on it. I guess she that was a round about way of saying I am a lying. Also, I was told that I never had a second night reservation (even thought I have an email with the ORIGiNAL reservation).
Marriott insiders be warned. I try to keep a sense of humor about it. This reminds be of the Tommy Boy scene - Tommyboy 04 Guarantee scene - YouTube
I had asked the issue to be escalated to Marriott senior management, but Marriott has be awful to deal with so I don't have high hopes...