Do large Hotel groups employ people to continuously evaluate and star
certify their hotels around the world?. Is there a star certification
body or organisation that rates hotels, if so how could I apply to
become one and what quaifications do I need?. Is there an Agency that
employs these certifiers worldwide?.

As I understand it, stars related to hotels names  ("four-star",
"five-star") refer more to the physical standard of the hotel:  if it
has a restaurant, bar, conference rooms, etc. The standards on this
vary from country to country, may be less tightly applied in some
parts of the world.
Thus I do not believe this something that is rated by having testers
checking the hotels the way the Michelin guide and other books do.


But someone could correct me on this.

AAA,Mobil,Zagats,Fodor and others have their own staff members who
rate hotels based on the criteria that organization or publication set
out.  There are some criteria that are the same but some will rate the
hotel on hotel amenities other will rate it on their experience at the
hotel.

Most of the employees who work for these companies are hotel
professionals who have many years in hotel operations.  Many are
retired and have the spare time to travel at a relaxed pace. This way
the company that hires this person has a fair judge based on a long
experience visiting a wide variety of hotels.

Therefore, there are no "hotel star certifier" classes to take.  I
would suggest you work at a hotel for a few years and see if the
industry is one you would like to be associated with.