Anyone can print a certificate. That doesn't make a dog a service dog.

That’s why the Americans with Disabilities Act directly says:

“Q17. Does the ADA require that service animals be certified as service animals?

A. No. Covered entities may not require documentation, such as proof that the animal has been certified, trained, or licensed as a service animal, as a condition for entry.

There are individuals and organizations that sell service animal certification or registration documents online. These documents do not convey any rights under the ADA and the Department of Justice does not recognize them as proof that the dog is a service animal.”

Not only does a certification system not exist, it can’t be asked for even IF someone got a fake one. People have shown the absurdity of the fake online certifications by registering a jar of Nutella as a service dog.

Businesses must ask the two allowed questions and can remove teams if they are out of control or have an accident.

Also from the ADA Frequently Asked Questions:

“Q7. What questions can a covered entity's employees ask to determine if a dog is a service animal?

A. In situations where it is not obvious that the dog is a service animal, staff may ask only two specific questions: (1) is the dog a service animal required because of a disability? and (2) what work or task has the dog been trained to perform? Staff are not allowed to request any documentation for the dog, require that the dog demonstrate its task, or inquire about the nature of the person’s disability.”

Read more here: https://www.ada.gov/resources/service-animals-faqs/