Don't be scared. A real service animal will be hardly noticeable. Hotels/b&bs are not permitted to charge guests for cleaning the hair or dander shed by a service animal. However, if a guest's service animal causes damages to a guest room, you are permitted to charge the same fee for damages as charged to other guests.
This might be helpful http://www.ada.gov/regs2010/service_animal_qa.html
Q27. What does under control mean? Do service animals have to be on a leash? Do they have to be quiet and not bark?
A. The ADA requires that service animals be under the control of the handler at all times. In most instances, the handler will be the individual with a disability or a third party who accompanies the individual with a disability. In the school (K-12) context and in similar settings, the school or similar entity may need to provide some assistance to enable a particular student to handle his or her service animal. The service animal must be harnessed, leashed, or tethered while in public places unless these devices interfere with the service animal's work or the person's disability prevents use of these devices. In that case, the person must use voice, signal, or other effective means to maintain control of the animal. For example, a person who uses a wheelchair may use a long, retractable leash to allow her service animal to pick up or retrieve items. She may not allow the dog to wander away from her and must maintain control of the dog, even if it is retrieving an item at a distance from her. Or, a returning veteran who has PTSD and has great difficulty entering unfamiliar spaces may have a dog that is trained to enter a space, check to see that no threats are there, and come back and signal that it is safe to enter. The dog must be off leash to do its job, but may be leashed at other times. Under control also means that a service animal should not be allowed to bark repeatedly in a lecture hall, theater, library, or other quiet place. However, if a dog barks just once, or barks because someone has provoked it, this would not mean that the dog is out of control.
Q28. What can my staff do when a service animal is being disruptive?
A. If a service animal is out of control and the handler does not take effective action to control it, staff may request that the animal be removed from the premises.
Q29. Are hotel guests allowed to leave their service animals in their hotel room when they leave the hotel?
A. No, the dog must be under the handler's control at all times.
