That would put my monthly payment around $1000, which would essentially kill my margin on this duplex.

for the last 12 months we've been working with CRE brokers to take down our first multi-family, everything we've seen locally has been pretty thin margins, so we've been sticking with single family. 

Profit margin, proximity to home, and the fact that it was mainly just cosmetic renovation.

I'd make sure you calculate a safe margin or error.

The asking price on the house is $96/sq ft and the comps range from $88 - $102/sq ft with only one, at $126/sq ft, that would indicate margin.

it was a foreclosure rescue of a 75 year old lady in poor health.. she wanted to live her life out in the home.I paid it off 80k and gave her a life estate.. she lived for 6 years.. by the time I took back over the house was beyond salvage I demod it subdivided it and am building 3 500k specs on it.. so my return on investment will be  well it will be more than 10% per annum by a long margin.. but I am thinkin I am in the business so I can find these kind of situations.. but how does a passive investor find them ?

With this kind of margin, all you're doing is delaying your flip profit and attempting to compound that with appreciation.

It's actually a low margin business.

If they are marginal, Hard money may be the better choice

I normally think long term is lower risk (occupancy, crazy renters, etc) but less margin when compared to short term.