Your behavior can be considered a waiver of the terms in the lease requiring rent on the first.  

There has been no behavior problem either.  

This is beyond unreasonable behavior. 

Given enough time and lots of good behavior, she'll be able to eventually improve her situation.

Then you are not open to all pets yet not closing off the possibility altogether....So, for example, one small well behaved dog you may approve  (especially one that a previous landlord says was not a noise, damage or other problem) but a pack of loud unruly ones not so much...And you can refine some of what you are looking for in terms of size, behavior, numbers, breeds, ages (no puppies without house training for me, eg), even spaded/neutered (especially for male cats, etc), references (ie how the owner did with a pet in past places), etc... 

To that end, you may request from the tenants that are being disturbed that they provide some documentation of the behavior that has occurred. 

You did the right thing.Next time just remember to meet him during business hours.People's behavior is always interesting when it is time to pay for a service, I have stopped assuming things.

I think that may be my best indicator by far of this specific dog's behavior.

There were expectations of responsible behavior, and consequences for breaches of discipline, and there was always an audience awaiting the outcome.  

We'd be having a "talk" about that behavior and hopefully come to an agreement right then and there, and document said agreement.