Never - they arent that dumb. They like Ambassador and Titanium guests. They would have to be a really dumb hotel to do that and Marriott would not take welll to it.

if it ever happend Id just charge it back with Amex and win easily.

4PM check out is GUARANTEED in their terms. They would defintey lose on a charge back but never once have they charged me. Frankly when I tell them Ill check out by 4PM id say 90% of the time they say sounds great and 10% of the time they say you cant. 90% of those times when I repeat it is guaranteed they drop it. Probably 5-7 times in 1000 stays I have simply stayed and kept the door locked when the maids came.

Never once have they charged anything. A charge o that sort would be fraud.