a. A service animal is a medical option. So is a wheelchair, a walker or a cane. Federal Law protects people's needs for these animals; they are not asking for a special privilege.
b. If you're a business owner who does not allow pets, please ask your animal-accompanied customer, "Is this your pet?" If they say, yes, then politely ask the customer to remove the animal. A service animal owner knows to say the animal is not a pet, and should let you know its doing a job. They won't always have a jacket on the animal, and there is no requirement to show "proof". If you have a complaint from anyone, you can say that the animal was identified as a service animal by its owner.
On the very rare occasion a service animal is disruptive or noisy, please investigate the cause of the disturbance first. The animal's tail may have been stepped on, for instance. A truly disruptive service animal may be removed from your premises.
b. Please don't ask anyone with a disability to tell you the nature of that disability. It's asking them to share medical information, and very impolite.
c. Please don't pet a service animal without the owner's permission. The animal has work to do, and must focus on its owner.
b. Please don't make loud, indirect comments about a person with a disability or their service animal. This is a form of bullying.