Duplex is residential building code so they are built to different standards. 

They may be rougher on properties than standard tenants but the cash flow potential is good, especially with a rent by room model.

This is standard in and around NYC.

We do it for our clients all the time.But an OOS investor should be careful as there are so many ways they can get taken advantage of:1) Buying the wrong property, wrong location, etc2) Being overcharged because there's no transparency on actual costs and budget3) Shoddy work because no pics/video are supplied4) Crappy tenants are placed that destroy the rennovationsNone of the above are discovered until an owner goes to refinance the property or sell it.What should an investor do to protect themselves?

As long as you know how to do the math - the numbers will tell you your answer:Conventional Loan purchase - 25% down = $40,000  + $10,000 rehab + closing costs (let's estimate $10k just to have something here) - TOTAL OUT OF POCKET = $60,0000HML Purchase - Lend 75% ARV (you didn't state this but this is pretty standard - if yours doesn't offer 75% of ARV then go find a different HML) - 75% of ARV = $172,500. 

If the tenant named in the lease moves out, the remaining occupant has no right to continue in occupancy without the landlord’s express consent.Landlords may limit the total number of people living in an apartment to comply with legal overcrowding standards (Real Property Law § 235-f)."

Often there are standards (ie goes to surviving spouse, if no spouse divided between all of the kids). 

Read some studies (but consider who paid for them and their motivation :-) And cities like LA, Seattle, NY cannot blame the vacation rental market for their housing problems, those are the result of failed policies by years of leadership....Vacation rentals have many benefits over standard rentals that you might consider a) they open up areas to vacationers that would ordinarily not be accessible (not everyone wants to stay in a hotel district).b) they almost always improve the neighborhood they are located in - the house, inside and out, must always be in near-perfect condition in order for the landlord/host to stay in business.

Then do those things, and whatever else you discover along that path that you "Didn't know that you didn't know".

I find it had to imagine the services of loan holding you to prior standard or Fannie/Freddie presumably the owner of the loan to request servicer to do so.