Perhaps if you really want to get involved with real estate you might want to consider looking into a REIT rather than physical properties so you can be hands off. 

You should NEVER involve the seller in ANYTHING after the sale, other than seller financing. 

However, if I worked with someone experienced like @Guillaume D. who hypothetically is very involved locally and was finding deals and had the know-how to flip a profit then theoretically would it even matter if it was Montreal or any other place? 

If multifamily is what you want to do I would stay involved and get educated on that.

I'm looking into potentially getting involved in Philadelphia real estate as I try to diversify my investing into different markets.

In fact, if you truly believe the tenant is involved with drugs evicting them should be one of your first priorities. 

Understand the fees involved and calculate the total cost for an entire year of management so you can compare the different managers.

The initial investment will be more involved.  

All of this anecdotal information tells me you are way to close and personally involved in this situation.

There's a word for that.With any lease involving more than one signer, include the words "jointly and severally" in your lease, along with a plain-language explanation of what the terms mean:  even if your co-tenant moves out, doesn't pay, causes damages, incurs violations or fines, etc, you are BOTH responsible.