It is my understanding that along with the two questions mentioned above:
For service animals, you should know you are only allowed to ask 2 questions to service animal owners:
1) is this animal YOUR service animal and
2) what service does your animal provide.
a trained service animal will not struggle on leash, is never left alone (i.e. in the room while the owner goes out), and is basically so well trained you would not know it is there.
You will know if a dog is not a true service dog. If it is misbehaving, pulling on leash, baring, peeing in the house, etc. I believe you can ask the guest to leave due to misrepresenting the animal as a service animal.
I have a guest coming Sunday who said she has a small service dog. I don't usually accept animals, due to my own, but we'll see on this one.
---> That's how I look at most guests, like cousins. And you know, some of those cousins are kooks.