I'm a 20 year Marriott Rewards member and have two upcoming trips to Las Vegas in May. I booked the first week at the Cosmopolitan on the strip at a rate of $150 a night. I went to book the second week, which is exactly one week later and the rate is $470 a night.
I called the hotel to ask why and was told that they were busy that week and that all hotels raise their rates when they are busy.
Personally I consider this price gouging and is something I would never do to my customers.