If you are the first to do the "only 2 rooms left" trick for example, you will get the full results before people get desensitized. But people will get desensitized everywhere, not just on your website, so if a competitor tries to pull the same trick, he won't get the same effect as you did. If fact, it may be time for you to roll back, to make competitors look bad for using the now well known and ineffective trick you invented. And if it works long term, then you get a head start.