The criteria for inclusion haven't changed since it started, about two years ago, but the meaning has shifted subtly. That sentence is probably baffling, so I'll explain a bit.
My list started mostly as an alternative to E-I's "Top Reviewed" list. That list has some problems. Bad reviews count the same as good reviews. Reviews from one time reviewers count the same as anyone else's. At the time I started, rats and n/a's were counted for the "Top Reviewed" list as well. So that list didn't really tell you much about quality, and it wasn't that difficult to cheat your way onto it.
I decided to set up a list by looking at escorts with a real track record, meaning non-n/a non-ratted reviews from established reviewers, and to pick the best reviewed rather the most reviewed from those. I designed it to be difficult to cheat your way onto it. It can be done, and I think in one or two cases it has been done, but you have to write dozens of fake reviews and get them past the reviews mods in order to do it.
In those days there were far fewer reviews in the system than there were now, so the weren't so many escorts with enough reviews from established reviewers to be considered. An escort needed a pretty good average rating to make the "top 50" list, but not amazing. If you count "very unhappy" as one star and "very happy" as five then an escort needed an average of about 4.4 stars to make the list. So at the beginning the list was mostly about genuine escorts with a good track records, but only those who were generally considered good service providers.
Now, with so many more reviews in the system, there are many more escorts who have enough reviews to be considered. Even though I've expanded the list from "top 50" to "top 100" it is much harder to get on the list now than it was then. Now an escort need an average rating of 4.8 stars to make the list. So the list is now about genuine escorts with not just good but amazing track records.
As a punter I am happy about that, or would be if I still lived in Ireland. It's a lot easier to find a good escort than it was even two years ago, though it can still be a problem outside the main population centres. As a list maintainer I'm somewhat worried. The name of the blog, "El Gordo's Guide to Reliable Escorts", is not as accurate as it was when I started. Back then, if an escort wasn't on the list then there were reasons to think twice before visiting. Perhaps she didn't have many reviews, or they weren't from reviewers with much of a track record, or the reviews that were from such reviewers weren't all that good. She might be great, but you couldn't rely on that, so it really was "El Gordo's Guide to Reliable Escorts". Now there are more and more escorts who are reliable by any reasonable definition of the word, but whose average rating is just not quite good enough to make the list. Also, it's too easy now for one curmudgeonly reviewer to push an escort off the list with a review which is not actually bad, but just ok.
Sorry for the long post, but sometimes there just isn't a simple answer to a simple question.