Not true. You obviously do not work as/with consultants/contractors. Some corporate rates will specifially say "no vendors" in the rate rules. Some rate rules will specifically say "ID reqd." On the other hand, there are times when contractor-specific or visitor rates are part of the corporate rate structure.

As for not caring about the rate you are paying, you most definitely have not worked with/for a client company as a contractor. I have had expenses challenged by clients when the difference was only $10 above their corporate rate.

The announcement of Marriott policing abuses of corporate rates was discussed a little over a year ago in this thread. At that time, Flyertalk had a sticky with the any known corporate rate code (which has since been removed). Many of the old codes will no longer show any availability on marriott.com. I find that they are still available if I call the reservation line or hotel directly. In all cases, I explicitly say "I will be doing consulting at XYZ corp..." when requesting the rate. At that point, I assume I am getting the proper rate category.

In the last year, I have been questioned a couple of times, but I have always been careful to bring documentation with me showing my affiliation with my host company and that was good enough. Interestingly, I have been challenged on the AAA rate (which is only a token discount) more than any deep discounted corporate rate, recently.