[yorkiemini]

Falsely claiming a dog is a service dog is considered fraud and is illegal.
Lately most airlines, and many other places ask for some type of documentation. Generally it is a document from their physician regarding their disability or documentation for a formal service dog school.
These letters address the disability act standards as well as the air carrier laws specifically.
Like many things it may seem unfair but it is unfortunately the law that requires specific behaviors.

I just came home from Westminster Dog Show and the airlines was much more formal and specific with with my Service Dog and there were a number of show dogs flying as well that were very well behaved. My disability is more recognizable than some and I have less problems than some other folks. But they will only allow so many dogs on a flight.