I’ve contacted BC Police (non emergency) due to potential animal abuse due to the conditions (He has a dog that I’ve even once seen with a cockroach crawling on its back) but they said there’s not much they can do and recommended me to go to Baltimore Code Enforcement.

I’ve been a real estate agent for a little over 2 years now in Charlotte NC where I was a police officer for 8 years before starting my real estate career.

Depending on the design style of your area you might be able to get away with the "industrial" look of a polished concrete floor but putting even 1/2in drywall on the ceiling is going to push you out of compliance.

Your best bet is to call the local PD and have them come out, verify with a walk through that the tenant left, and get a police report to verify that for your records. 

For the locals in the area that might be able to help pinpoint areas of focus here --- think if you were an established hard working professional (not CEO or independently wealthy)  working at for example -- Redstone Arsenal, NASA, Military, one of the Universities or major Hospitals, the airport, a local lawyer, dentist, fireman, police, teacher, business manager, small business owner, corporate executive, etc, etc..  

Assuming you have your "ideal renter criteria" fine tuned and polished, pre-screening questions can help to weed out unqualified applicants.

Does that considered an illegal action and he can call the police on me?

I’m a police officer out here as well so I see a lot of things first hand- there are some neighborhoods in Brooklyn (SI too) that are riddled with so much crime, drugs and violence that I wouldn’t take a house in even if it was free. 

I am a veteran and full time police officer so I've heard they have some special programs that help us out.  

I was a Peoria Police Officer for 13 years, my last 3 as a violent crimes detective.