If you are compiling information for a mailing list, I would use one of the services that has an algorithm to calculate equity (such as ListSource).

I'm pretty good at it, I use a computer algorithm and the Assessor's data.

Their "Zestimates" seem to me to be a blatant attempt to fan the flames of the market -- after all, who could resist buying a $78k house "worth" $468k.Rural or neighborhoods with a variety of home types/conditions are particularly confusing for their algorithms, though goodness knows I would have dearly loved to sell my MH for the $379K they said it was worth shortly after I purchased it for $60k!

The algorithm on how they calculate their numbers is on this page.

I am wondering if anyone here has done a deep dive on their algorithms / tools to see how reliable they actually are (after all the 1% is a rule of thumb, right?). 

The SEO approach, no matter how good you are, is always limited to whether people search for your keywords or not, and whether google shows them your message or someone else's based on their algorithm of the day.

Do you have an algorithm that you could share when screening triple NNN properties, or minimum 5 sq mile population?

However, I was not great at using the algorithm to my advantage for pricing, so the overall income was not what it should have been for the first year.

It is an algorithm.

I don't know how their algorithm works, but seeing as they can only use the data that was self-reported, I'm assuming that in these three situations their numbers are way off.