This puts upward pressure on rents, and should not be discounted. 

I'm comfortable with knowing that it could make it more difficult to sell in the future, however I would be purchasing it at a discount now so that part feels like a wash.

That is a tricky situation but you could implement stricter tenant screening processes, implement strict rules and consequences for tenants who violate the terms of their lease, try to work with the owners of the surrounding properties to address the issue of problematic tenants, offer incentives for good tenants such as rent discounts or referral bonuses, and consider partnering with local organizations or community groups to improve the area and make it more attractive to potential tenants.

That in and of itself is a huge achievement and shouldn’t be discounted just because there are so many out there touting the benefits of multifamily and economies of scale.

Couldn't you just work as a buyer's agent for a rehabber/landlord and charge the rehabber/landlord a commission if you get them a good discounted deal? 

I have bought a non performing 2nd at a steep discount and got the owner performing again (42% return).

Hi everyone, I'm curious to get insight from experienced investors on their most effective strategy in finding off-market/discounted deals.

Properties that are in a state such that they can only be bought with cash (or maybe with a construction loan) are automatically going to go at a discount. 

There are a lot of details in the tax lien business and the rules vary tremendously by state and even county.

Did you use a discount broker or something?