How can a hotel be rated at 3 star by one source but 2 star by another?

Hotels worldwide are rated on a 5-star system with 1 being the most basic and 5 the most luxurious. Seems simple, and it would be simple if there was only one organization or “hotel rating authority” that assigned the stars globally, but that’s not the case. Here in the U.S. not only does Mobil assign stars and AAA assign coveted diamonds, but Trip Advisor, Orbitz, Hotels.com, Travelocity, etc., etc., etc., all have their own rating systems as well. Even travel bloggers get into the act, and hotels are free to choose the best rating and advertise that one. In assessing what a rating means it’s important to know the source. In the U.S. the gold standard is the AAA Diamond program. Having any diamonds is a good sign because AAA doesn’t “approve” poor quality hotels, and the more diamonds the more luxurious. In other countries the most definitive ratings may come from different sources, and often from that country’s government or hotel industry association. These ratings generally reflect specific designs and amenities and have nothing to do with the level of customer service, charm, ambiance, etc.