Rentometer is just an algorithm and it is not exact by any means.  

Their algorithm is pretty crap.

All STR sites use an algorithm, which isn't solely based on the cheapest price, but all sorts of things, like reviews, "turn downs" (like if you turn down a customer for ANY reason at all), options (business ready, superhost, instant check-in, etc), and even how fast you reply to your customer.

Often they look at generic numbers for an area and then just put an algorithm on it to adjust for years at a time.

You can also look at Redfin or Zillow to get their price opinion (though look carefully the numbers are based on a algorithm)Finally ask a local Realtor to give you an idea how the market is locally, is it hot or cold?  

In Texas and any other state where "sold" values are kept private, services like Zillow has to do a lot of guessing with algorithms.

The algorithms and table formats are the same for both.

I think your algorithm is too simplistic.

Also are investors doing this manually or are there algorithmic/ robot services that are snapping up these offerings?

That's a loan I do as a favor to a referral source, not something I'm hungry for.620-675 is the range where FICO's algorithm might not be accurately picking up someone's creditworthiness & I'm happy to help, but 580 means someone's life is a total mess, but they have delusions of homeownership.