For most places, it is actually illegal for businesses to demand proof that the dogs are certificated hearing dogs.
My friend has two dogs-- one is actually Hearing dog (and is spoiled as a pet) and another a pet. She took them everywhere and used orange leashes to ward off any inquires. Sometimes she will have me or her Deaf boyfriend to take one dog just to make it subtle-- i mean, two hearing dogs for one Deaf person? HA!
She knew she was abusing the power but she was never home (from midnight to 9am) so it was her way of taking care of her dogs by taking them everywhere with her.
My cat is acting as my "hearing pet"--he doesn't run away when doorbell or knock.. he ACTUALLY ran up to the door and went "meow meow" just like a dog would go "woof woof"....
He even signals if a car is pulling into our driveway. VERY GOOD CAT! (pat pat!)
