I recently had a friend approach me with this concept. 

The concept is known as adverse selection.Don't know for sure, but I would guess that is the case.

There are negatives to this approach (mainly living next door to tenants), but works for many.

Michael, we did not have a lot of negative surprises on this one.  

I was recently introduced to the concept of investing in tax lien certificates.  

It's not the best investment per se, as the cash flow is negative, but we had to get a bigger place with a baby on the way, and it's underwater so we couldn't sell. 

This theory sounds good on paper but I know very few people to actually do this with success [except @Brandon Turner ].To complicate matters further, you are looking at an attached double, which are rare here in Indianapolis, that is zoned as two separate properties.As mentioned earlier, this defeats the "benefits" of having two doors under one roof/deed.In addition, this type of property is tough to resell in the future as well.I'd suggest passing on this one and whole concept - IMHO.  

Some who used to do it say it led to negative relationships with other Realtors.Is there a service out there that can put a listing on the local MLS?

The market in the neighborhood is about $83 to $85 per foot, but I have two major negatives in my floor plan--lack of a fourth bed in a 2000 plus sqft house and all beds up so I will have some significant downward adjustments despite having the finishes that are considered quality in that neighborhood.  

There are 2-4 unit properties in the Dayton area that would have negative cashflow, even with 20% down and self managing.