You sound very much like us. And they definitely manipulate availability to maximize revenue. I often see that if I want to book 2 nights, there is no availability. If I make it 5 nights, rooms magically open, including the two nights that were previously unavailable. Or switch to arriving mid-week instead of a Friday. When they changed their reservation system so that you cannot just add or drop nights from your reservation, and instead made it so that the entire new reservation has to be available, (even if the new dates were included in your original dates), it was to maximize revenue.