Unfortunately we haven't played each other yet, but I've tried to Green Thumb you several times(but couldn't) because I am so grateful for giving us KoT. Hopefully I can soon. IMO most devs should be green thumbed as they would not be doing this if they weren't reliable players themselves.
So back on topic, everyone has their own personal way of rating people, a personal treshold they have to reach.
See it like this, often people have to rate customer service from 0 to 10, but even when everything went perfect, couldn't screw up and couldn't improve, some people are adamant to only give a 9 at the most. When asked, why not a 10, and what could be improved to reach that 10, no single person could answer. Everyone just has a different style of how and who they rate, and that's okay-ish. besides, it's just a virtual platform and plenty of other people to play with.
I myself green thumb people everytime either they really played a good game(good moves, good timing, something nice said in chat, etc...), or when I play them and say "hey, I played this person before". So if I recognize that person as having played them multiple times without memories of bad play, you're a player I can recommend. Has nothing to do with skill level, but it is a player that doesn't let you down.
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and other times not so much.. 
