I wish there was a system for searching for STR specific things but I have only found something like AirDNA to be the closest even though it's far from ideal for that.

Are there specific metrics or tools you rely on?

Most foreign buyers are high net worth individuals who want to park their money there in a safe haven and they don't need BP.No restrictions apply to American buyers in the countries they'd generally want to buy, including those mentioned by Federico and many other popular countries.When it comes to Spain specifically, some more conservative banks will ask you for a 40% downpayment (that would be the maximum) but that isn't the rule.

Numbers are very specific to the market you are looking at.  

Is it from experience of there are tools out there that show numbers on specific areas?

You point out specifically "... on forum run by his publisher." 

Cleaner is paid a fixed rate for a specific job, you are paid a % of revenue.

How specifically could they have done that?

My biggest advice for people would be as follows.Know why your in the real estate game, and why a specific niche.

From my experience, attending local meetups, lending-specific events, and networking with experienced investors can open doors.