As a deaf person, this is something I see/hear all the time... I have a friend who has a 125 pounder yellow lab mixed breed. He told me that the dog travels with him, and I said so you paid $100 each time, and he retorted, no it is free. After questioning him, he said he would just walk up and claim the dog is a service dog just because he is deaf and the airline cannot do $hit.
I always tell people that if they really believe in doing the right thing, they would not pull this kind of BS, but being the cheapskates that deaf people are, they always pull this crap.
It is no wonder managers purposefully do NOT hire deaf people and would go measures to violate the ADA [as in not hiring us SOLELY based on us being deaf and requiring additional resources like interpreters and videophones, which translates into our favorite word, "costs"] and simply not hire us even though we are more than qualified for the job.
This situation, whether the customer is deaf or not, is a perfect example of a pure intention to abuse the ADA. I honestly wish that ALL service animal MUST be certified and that those owners MUST present some kind of documentation to prove that the animal is trained [from an authorized animal trainer] along with a doctor's note stating that the certain individual needs such service. With those kind of requirements, I am pretty confident the volume of abuse will shrink dramatically.