How can you tell if a service dog is fake?

Owner Doug Stabler recorded video when a customer walked into the ATV Warehouse in Sacramento with her dog.

"The dog paused for a second, lifted a leg and just left a big mess. Just asked the lady if her dog was a service dog and she said 'yes!" he said

But Stabler says he saw the dog pee on the floor - and had his doubts that the woman was telling the truth.

"I don't think this is a service dog. It's not acting correctly,” he said.

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But how can businesses know if the service dog is legit?

The American Disabilities Act - says you can't ask a dog owner about the nature of their disability, only about the tasks the dog will perform.

Wendy Clock-Johnson has been training service dogs for 9 years.

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"Their focus should be on what their person is doing and what their person needs,” she said.

This can include turning on light switches or pushing a wheelchair, and she says their manners should be impeccable.

"When the dog is out in public they shouldn't be sniffing the floors or licking the underside of the table,” she said.

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But even with roughly 18 months of training, owners in California - don't have to display the dog's certification. Stabler calls that a mistake.

"I want to make sure that this thing has been trained and licensed,” he said.

He says incidents like this give real service dogs a bad reputation.

"You would hope that people would not try to pass the animal off as a service animal if it is not,” he said.

Pat McConahay with Disability Rights California says an instance like this shouldn't take away from the important purpose served by service animals.

"It may not be obvious or visible but they are a very, very important thing for people with disabilities,” he said.