This is the exact situation that the Guarantee is supposed to apply to. Properties overbook, since sometimes guests with reservations don't show. For example, you have 100 rooms and if 5% of the people don't show on a given day, you can maximize revenue by booking up to 105 rooms, and pocketing the extra revenue.

The front desk checks in people as they arrive and when all 100 rooms are occupied, the hotel is full. I don't expect them to turn away another guest that arrives before me, assuming I haven't checked in yet. So when I show up and become guest 101, they have no choice but to walk me.

Regardless of brand, most hotels will find a reserved guest another room at the hotel's own expense, since they have taken a guaranteed reservation they cannot fulfill. Elite guests get additional compensation, which for Marriott is outlined in the terms and conditions. Yeah, this could get expensive for a hotel if they owe $100-200 + 90k points (or whatever is called for by the terms and conditions). It's the same with airlines and bumps -- all due to overbooking which is a revenue maximization tool.

For better or worse, some of the overbooking is a necessary evil -- people's flights get canceled or delayed, and in my experience I have only had one instance where a property didn't just cancel (or modify) the reservation and I wasn't charged for the missed first night (admittedly, I call the Marriott Bonvoy line and typically not the property directly). So if I end up getting walked one late-arrival day, I would completely understand -- but would expect the compensation to be paid according to the T&Cs.

I appreciate the comments above about chatting with the front desk, but honestly my chat experience with the 10 or so properties I tried it with is very hit-and-miss. Often I get no reply, or sometimes a reply the following day asking me to come to the front desk (these weren't complex requests) or to call housekeeping myself. Often my pre-arrival requests are to confirm a late arrival, and asking the hotel to please hold a room with a certain bedding configuration (Queens if we are traveling with one or more of my kids).

I would also suggest checking in online when arriving late -- ONCE YOU KNOW FOR SURE YOU WILL GET THERE. If my flight is delayed, I will not check in before we get airborne as once I check in, I have lost any option if the flight gets cancelled or delayed until the next day.