If one knows how to lease properties effectively and efficiently and can identify niches then you are well on your way, especially for buy and hold. 

Take a given City, no matter whether its high prices like San Francisco or lower price points like Cleveland, what is the most/least efficient segment of the market in terms of pricing?

Be quick and efficient with their property concerns such as maintenance matter.3.

Not as efficient as new boilers but they'll last much longer.

One reason I ask is 400 units in 50,000 sf can range from ~90 sf per locker (assuming 72% efficiency layout) on average, up to 125 sf if a drive up facility.  125 sf per locker is on average large lockers.  

Strip out the (largely offsetting) impacts from the typically volatile food and energy sectors, and "core" prices still declined 0.1% in May.

., efficiency, one bedroom, two bedrooms, etc.) of affordable housing dwelling units in the building and the contract rent for every dwelling unit in the building.

On a 16-unit you'll realize some efficiencies of scale, so could knock that down a couple of percentage points.

On top of that, you will want to account for higher returns on a D-class investment to account for the additional time, stress and energy, and the fundamental additional risk associated with it. 

A month has gone by and she realized that her DIY method was not efficient and she tried booking a professional to treat it and she kept getting told that the owner needs to call to make the appointment.