Some, but not all, service dogs wear special collars and harnesses. Some, but not all, are licensed or certified and have identification papers. If you are not certain whether an animal is a service dog, you may ask the person who has the animal if it is a service dog required because of a disability. In rare circumstances, a service dog may be excluded by a place of public accommodation when that animal's presence or behavior poses a direct threat to the health and safety of others or causes a fundamental alteration in the nature of goods and services provided. Explain that the ADA protects the right of a person with a disability to be accompanied by a service dog in public places.
Some dogs come from breeders while others are rescued from shelters.
The sources for these dogs are just as diverse as the breeds used. The breed of the dog is not as important as the dog's ability to learn. However, some breeds are more commonly trained as service dogs than others. These include golden retrievers, German shepherds, and Labradors.