Now, over a year and a half later, he sent a certified letter last week demanding the security deposit or legal action within 30 days.Please advise. 

I sent her a 5 day notice via certified mail with return receipt requested because she wouldn't answer the door or answer my phone.

There are plenty of great renters aside from travel nurses looking to rent by the room and most will be outside of the healthcare field.To your questions:If the home will be furnished,  Furnished Finder will need to be amongst those that you use.Other top platforms: FB Marketplace, Zillow, Roomster, Airbnb, Nextdoor.  

While Facebook Marketplace isn't the sketchiest site (craigslist), I personally would never give my ID across it.

I will say anyone offering this should be giving you all the pros and risks of the flint marketplace.

you can also go here https://www.nachi.org/certified-inspectors/near/des-moines--... and search for inspectors as well. 

I do see lots of self storage and warehouses going up, so my default assumption would be that the old shopping malls do NOT trade for less than build cost, but it's possible that the marketplace is not perfectly efficient. 

Advanced QuickBooks ProAdvisor was introduced in 2007, to get certified the requirement was: one had to be certified for 3 years in a row and had to attend 2 day in person and online courses.

I don't know NY law, but in AZ, you may send two certified letters. 

Meetup.com is a good resource for those but some of the groups will also post here on Bigger Pockets Marketplace too.