She says this is not a pet, its a service dog. 

Did the previous tenants have pets because if they moved in one day ago I am going to bet on fleas and you need to bomb the place. 

In a local Facebook group, landlords and prospective tenants advertise their units or looking to rent a unit however today there was a discussion on there of tenant's complaining that most landlords in the area don't allow pets and several people said they registered their pet(s) as service animals and insist they can't be denied because of it.

They have very high incomes, long length of employment at current employer and no pets.  

Specializing in rural college student rentals with horses/pets.

That was one of our first rentals and a mistake we never made again.At minimum, you'll need:Rental application (BP has some samples)LeaseLease addenda (drug use, specific cleaning stuff, flammables in detail, pet stuff--whatever)Walk-through forms that have room to write down any issues and initial it (btw--we take pictures and put the pictures and a scanned copy of the walkthrough in Dropbox and e-mail the tenants a link).  

We established a NO pet policy many years ago and recently a tenant secured a Service dog because of a trauma she suffered.

Think of all the things that could go wrong and see if the lease addresses them: unauthorized pets or tenants, early termination, security deposit, lease violations, late rent, eviction, lawn maintenance, parking, etc.5.

@Sam Leon I've created addendums to my leases many times for different reasons, like changing the mailing address for rent due or the addition of a pet.

I know my kids and my pets...