This doesn't surprise me though, as properties in Costa Rica are way less profitable than people think they are.

EDUCATE YOURSELF - yes, it will take time, but will lead to a selection that better meets your expectations & avoids potentially costly surprises!

Honestly, my only surprise in it is that it hasn't happened yet.

That is a chance that the two you exited are actually better projects with better results - that's why it was exited..The others might have surprises..Hope that's not the case though.Secondly, most hands-on investors made way more than 20%+ IRR in the last few years.You can always hire people to manage your ph calls.Active can never beat passive, as long you are reasonably smart.

Wait a few more years and I would not be surprised if every SFH can be converted to a quad.  

I use DealMachine, and I'm happy with it (I read the instructions you provide at the site, so I actually wasn't surprised by anything).

Windows would be my next check-point (less than R1) and then wall insulation: I would not be surprised if they have no insulation inside, but you can do blow-in, which only requires a small hole.A home looses heat in two ways: heat conduction (which you can slow down with insulation) and drafts, which in old houses is usually the biggest culprit.

I'm surprised to see so many posts favoring blinds over curtains.

Best way to do this, you want it to be a surprise so you see how they really live, is to setup a Zoom call with them at home to go over some "questions".

Their are opportunities but very much depends on location, no surprise there.