re: Question about the aforementioned service dog

Actually the animal can't block access and can't sit in a seat. The Great Dane would have issues flying.

You can ask two questions of service dog people. If the dog is required for a disability and what service does the dog provide.

Comfort dogs are not service dogs. If the dogs purpose is solely to provide comfort, it does not get the same protections as a service dog. If the dog is trained to alert the owner or others to an anxiety attack, that is an example of a service dog. It serves to perform a service, not merely being there to comfort. Airplanes don't have to allow comfort animals and public places don't have to allow them either unless there is state laws that apply.

Also if the dog is uncontrollable or is an issue/untrained, it doesn't matter if it is a service dog, you may request that person to leave. This also applies to not being house broken, you may immediately ask them to leave.