is that not established after construction once the hotel has a chance to serve customers and pay the appropriate bribes to the judging committee?

5 star hotels have pleasure pods. 

The difference is that 3 star hotels serve stale bagels at their complimentary breakfast bar.       5 star hotels have crepes and shit.  

In a 3 star hotel the roaches live in the 3 star hotel. In a 5 star hotel the roaches live in their own hotel.

this isn't standardized; the rating systems vary in different places (and a single hotel can have multiple ratings by different organizations); and many of the criteria are subjective or related to service not design.

Typically it's up to the hotel operator to determine what ratings they target and brief the designer on what design standards to follow in order to achieve it.

https://en.m.wikipedia.org/wiki/Hotel_rating

The highly subjective rating is determined largely by the quality of attention the staff gives the guests. You, as an architect, can't possibly know what rating your hotel will be. 

Star ratings in hospitality are very subjective, not defined in any objective way, and depend on a whole lot of different things. Probably the three biggest factors are Accommodations, Amenities, and Services.

Typically, a 3-star hotel is focused on price-conscious short-term utility travelers and families (in tourist locations). Think budget conscious business travelers, overnight layovers in transit, and that kind of thing. Accommodations are comfortable but not spacious. There are few amenities, and services are fairly bare-bones and tailored to that transient clientele. While suites are found in 3-star hotels, they are not common. 3-star hotels typically do not have in-house food preparation or restaurants, though they may offer low-end "continental breakfast."

A 4-star hotel will be for higher-end (but not top-end) business travelers, vacationing couples/families (if tourist oriented). Rooms are larger and better appointed, often with additional accommodation features (like work desks, sitting areas, etc.), and a larger proportion will be suites. Many more amenities (gyms, spas, business centers, game rooms, etc.) will be provided for guests. A 4-star hotel will have food prep, room service, and probably at least one restaurant (possibly two or more, focused on different clientele). Some 4-star hotels may have banquet and conference facilities. The range of services will be wider and more personalized.

A 5-star hotel is for top-end business travelers and luxury-oriented tourists. Rooms are luxuriously appointed and mostly suites, with separate areas for sleeping and waking activities. Amenities are similarly luxurious and focused on pampering guests. Services are extensive and personal. At the very highest end, each suite will come with a butler. Quality of accommodation and service is more important to customers of 5-star hotels than price.

Beyond that, there are hotels which advertise themselves as 6-star, and even one 7-star (the Burj al Arab in Dubai). They are just more extreme examples of what I described as a 5-star.

At the low end, a 1-star would basically be a hostel or a flop-house. A 2-star is basically an old roadside motel.

Hope that helps. There's a lot more to it than that, but it should give you a basic idea.

A 69-star hotel. Wonder what that looks like