Now the identical sister building is going to be up for So I recently bought a foreclosure duplex that was built in the early 1900's for $260k.

I have posted identical advice several times here on BP.

But, I saw an identical unit with the same floor plan in the same complex on Craigslist rent for $2750 so I figure the market rent is about $2750.

It's like finding a needle in a haystack just to locate the target property...and then you need to find at least 3 other almost identical, sold "comparables" to prove your good deal and current market price...and still be at least 30% below fair market value for nearby residential listings (on top of deducting necessary repair expenses), and at least 40% for an REO...and don't think you can submit a deal for vacant land, commercial or anything else that is not a standard family residence.

Last year when Amazon built a 1 million square foot center here home prices went up a lot.I am hoping this corrects the recent downturn, this means there will be quite a few management people from that center looking for nice homes in the area to buy.There has also been talks of another 1.5 million square foot facility being built soon but they always keep the identity of the place secret until they are ready to break ground.

There are 4 more 4 plex's for sale on the same street that are identical.

I was thinking of possibly taking out ~$50k which would make my monthly payments almost identical to what they are now. 

The floorplan is identical minus a 4th bedroom where I have a loft...

Those three, let's say identical buildings could have vastly different NOI's. 

You must first have knowledge, a plan, a business plan, a identity and somewhere along the way either at the beginning or sometime later create the entity that fits your individual need and end result.