The law is you can ask what the service dog is trained to do. If they say it is a service dog, you have to let them in. However, if the dog bites someone, for example, and it is deemed that the dog is not a service animal, the owner and not the business is liable. The real kicker is people claiming emotional support animals are service animals and they are not protected by the Americans with Disabilities Act. If you ever question these people, they go psycho.