I agree this is an issue being created by Airbnb mixed policies. On one hand they tell Guests to check with Host on pets prior to booking, then under service animals it states even without notice Hosts must accept. We just had a Guest who brought a large "service animal" unannounced, left in house alone at times, and we only found out when neighbor advised us of a large dog staying at premises. Our policy clearly states non-shedding, small dogs with prior approval.
The Guest responded with the Airbnb policy that they did not have to inform and they have done this several times in past without a problem. We would not have even known except for neighbor who knew our policy for renting. We understand the need people have for special service dogs but there should be required clear communications.
In my opinion Hosts should have the ability to say yes or no. Airbnb says they do not consider service animals (dogs or small horse) as pets since they perform work or tasks for people with disabilities. Airbnb evidently considers them like butler or maids that walk like animals, shed like animals, excrete like animals, bark like animals, etc.. So whether considered as pets or not they have all the same maintenance issues as animals for Hosts.
Guest is technically correct and stretching communications required to the limits, so we are going to contact Airbnb on confusion they are creating.