The Massachusetts Attorney General's Office provides a useful webpage answering many of the important compliance questions that businesses have.
A couple notable statements that I would draw attention to: "Currently, there is no state or national certification available for service animals so businesses are not permitted to inquire if the animal is licensed or certified or whether the animal has identification papers."
Also: "To differentiate between pets and service animals, businesses can ask the person with a disability if the animal is a service animal required because of a disability. They can also ask what tasks the animal has been trained to perform. Once an individual answers these questions the business may not question them further or separate the animal from the individual except as noted above. Businesses may not inquire about the individual’s disability."
The underlying body of law rests on the principle that persons with disabilities should have access to businesses and public spaces. In turn, businesses and offices should probably use policies that favor access over restrictions.