Today was the last straw when my electrician was in to do some work and reported there is now a cat in the apartment (no pet policy).

If the floor has pet stains, handle it Nicole Curtis style and stain it dark and the dark spots will just look like a variation in the stain.Check the sub-floor.

One of my pet peeves is feeling like I'm being taken advantage of, and while I truly hope that's not the case, many here have commented that this is exactly what is happening.  

One of my pet peeves is the guys who start out trying to sell as service on something they haven't perfected.

By inheriting a tenant, you get a sneak peek as to how clean they are since you presumably did several walk throughs during the purchase period (being able to see pets, etc), and if they pay in full, on time (viewed during your due diligence period).Similar to your situation, we have bought 3 SFHs with existing tenants, and within each of which, the rents were significantly under market value. 

At that point it is virtually waterproof so even with pets it holds up really well.

I saw He also acquired a pet a snarling aggressive 150 pound pit bull tied up to a logging chain in the back yard .

You can present all the information you gathered from the seller as far as leases, security deposits, pet deposits so forth and so on.

I would require a $250 pet fee for this.  

I also only allow a well-trained family dog with a minimum 2-year lease as it's not worth the risk of a pet for a one-year term, especially in a newly renovated home.