The one guy I spoke with said they make money only when they sell to potential investors and they only sell new construction homes that are usually pre-leased to buyers (currently they are building in Texas state and Missouri State).

This is not the case for the majority of metro areas across the US.In less hyperbolic markets there wasn’t an intense amount of speculation so operators didn’t pay high and are weathering the storm on interest rate resets and are finding a way to refinance Deals with maturity walls.I am finding that a lot of killer deals with my clients are happening in the sub 50 unit deal space for those who need to sell, because there’s much less competition in a chase for yield.  

How can you sell it. does the original owner needs to sign any docs to do that?

I've been using the MLS, but I like the idea of talking to neighbors to see if they’re interested in selling—or at least getting on their radar.

I can get her to sell to me for the current mortgage balance of$150k'ish.

A member of the association who is not on the board would probably not even know if they were selling.

As for your current home I would weigh the value of renting vs selling.

In case I have to sell or I quit running STRs I wouldn't want to be under water out the gate.

Most people don't start looking until the the settle on the relinquished property, start earlier! 

Some people do SOI, some people do mailers, some cold call, and some do events..