The op's experience is actually quite a common occurence for guests who are hand picked by properties to be "marketers."

I can vouch that Starwood in using TNS actually has TNS people going to some of their properties to do spot checks.

Cinemas also have people who do spot checks on trailers and advertisements.

As to the question of anonymity, what is probably the case is that the front desk clersk are told duirng a certain period or duirng a day that there is a "mystery guest" evaluator. The person's name may not revealed.

So the front desk clerk do know that they have a mystery guest but as to you specifically, unless you behave in a way that is obvious like taking out a pen and deliberately copying everythign in full view of the staff, they will most probably not know its you.

I done it before on a frequent basis for a certain brand, that is all i will say.

The criteria for selection however remains secret...

cheers