The system was long known as the Mobil Guide, launched in 1958 and (according to Wikipedia) the oldest travel rating guide in the US. Now known as the Forbes Travel Guide, it still employs the same detailed methodology of incognito, expert inspectors paying their own way and running through amazingly detailed checklists covering all sorts of obvious and obscure guest details.
FORBES: Peninsula Earns 5-Star Sweep, Other Luxury Chains Close Behind