Yes-also some hotels have ' long term ' rates. Lower if you stay 4 or 5 nights. Cut down to 3 and your rate goes up.

To the extent there was a contract (as opposed to an offer), it was for 5 nights. There was never a contract for 4 nights, so the hotel didn't change the rate on that contract.
The customer assumed that the rate wouldn't change, and maybe it wasn't communicated clearly (although every reservation I've seen always says something about early departures may result in changes). But that's a customer service issue- not a legal issue in the guise of a contract. If you had a rate you negotiated to buy 1000 widgets at $10 a piece, you couldn't send back 999 and insist you only owed $10 and not a dime more, as the price was negotiated based on the quantity. There was no contract for 1 widget, and thus the default price would be the market price.

Yeah, my experience with Marriott is that many properties, particularly extended stay brands, give a nice discount for 5+ day stays and that those rates are clearly labeled as extended stay rates.

The key words printed in EVERY hotel booking confirmation for Marriott: Please note that a change in the length or dates of your reservation may result in a rate change. They're on the website during the booking process and on the confirmation email.

You may have a leg to stand on if during check-in you told them up front you were staying one less day and the FDA affirmatively told you there would be no rate change. But good luck proving that - it's the FDA's word against yours.

-RM

"May" is the key word here. To me, the word "may" means that there is a chance for the price to change. But there is also a chance that it will not. It should have been the employee's responsibility to inform the customer of the change.

In contracts, there is a concept called "Contra proferentem". When there is ambiguity in a contract, you interpret it in factor of the party that did not write the contract. Marriott is who wrote the contract, not the customer. Marriott can change/clarify its wording at anytime. In this case, that means the contract should be interpreted in a way that favors the customer.

I have an upcoming 4 night stay at a run of the mill Marriott property. My reservation states that there will be a $150 fee for checking out early. Not sure if the nightly rates would change, however. The OP's experience is a cautionary tale as much as it sucks.

The Hotel can do this, you effectively nullified the contract and did not agree new terms, so they are free to use BAR. I understand the FD said no problem, but unfortunately
you have no evidence of this.

Live and learn unfortunately. You say this has never happened before, have you made this mistake a number of times ?

Yes

If there is no contract, then it is up to a neutral party (such a a judge) to determine what is fair. Can a hotel state that they are going to charge you $100,000 a night? That is completely unreasonable.

Because the terms and conditions state clearly that in this situation the Hotel CAN apply BAR, this has been quoted a couple of times up thread.

​​​​​​Its only up to a judge if they have to sue to collect for nonpayment, and if there is no contract, the result would be quantum meruit- the rates that the OP were charged were likely the going rate, and therefore exactly what the OP was charged.

​​​​​​at best, this is a creative argument but not one that would pass muster.
There is no ambiguity in a contract to interpret: the contract was voided by the customer who decided they no longer wanted what they agreed to terms to buy. The number of nights is plainly a material term, and there is no ambiguity about that

Sure enough, the GM’s response on TA for OP’s stay precisely mirrors the feedback already given here:

​​​​​​
Hmmm. You're unto something here....

But how I WISH it would be the case for all of us that we book an extended stay rate or a promo rate that's much cheaper if we book a minimum number of nights and then at check in, say "oh I made a 'mistake', I'd like to shorten the reservation for 1 or 2 nights instead of X number of nights with the same rate."

And when was this mistake known? I would have changed the reservation asap instead of winging it at check-in if I didn't have a hidden agenda.

Reading through the GM's responses seems to me Paul is a reasonable person