According to the Mystery Shopping Providers Association (MSPA) there are some 30, 000 of them in the U.S., hired by luxury hotel brands to check-in anonymously and judge mercilessly.

CNN: Confessions of a hotel mystery shopper

"In the late 1980s, Hilton was among the first luxury hotel brands to utilize the service, " says Mike Bare, co-owner and president of Bare International and one of the original founders of the MSPA. Three decades later, it's common practice among hotel brands around the world. (Proof: LRA recently opened a satellite office in busy Singapore.) And soon enough, its taciturn nature may be over.

CNN: Confessions of a hotel mystery shopper