Same reason why an agent may push a seller into accepting $10k less on an offer, it gets the house sold and the difference is only $300 to them (based on 3% commission), whereas it's $9,700 to the seller. 

I am located in the north shore area of MA and got my two duplexes through house hacking but always will to share my experiences! 

All roomates are responsible for the total rent unless you rent by the room for a rooming house.

20k will maybe cover a 5% down loan a 400k house. 

The first one is a 3 bedroom 1 bath house on 1.67 acres.

Moisture in ceiling; subfloor damage.Moisture in ceiling; staining and previous repairs.Moisture in baseboard and floor.Moisture in ceiling; staining.Moisture in ceiling.Roof replacement; address moisture and leaks.Exterior inspection; identify and fix moisture sources.Fix moisture damage.Electrical system overhaul; ensure safety and compliance.Temporary housing costs for tenants during repairs.

They claim to have owned four rental properties and a large house which they sold before coming here.

I have bought and sold over 1,000 properties for my own inventory, and did Bigger Pockets Podcast #82, and have spoken coast to coast from Manhattan to San Francisco on real estate topics, and wrote a book on my experiences.So I can't say I did it all on SFH, but renting houses has been a big part of my real estate investments since I first started investing.

Podcasters that does house walk throughs will sometimes say, "if this Floorplan isn't available in your city/state"  blah blah blah.

An example problem statement that I may have stated (and built the software for) in 2003, when I started investing full time: Build a tool for lead generation that collects county records from the county recorder's office (and property card data), finds the recent first mortgage defaults  from trustees websites or public filings for properties that are between 1000 and 1700 square feet, in a neighborhood of 90% like-kind properties with greater than 20 parcels, houses built after 1978, that can cash flow at current rates when fully leveraged.