At a glance, it looks like the false friend of "to fart", isn't it? Actually, I also don't know how to explain "farti" because in esperantujo, everyone says "Kiel vi fartas?" as "How are you?". "Kiel vi estas?" only makes sense for English speakers. There are things that cannot be translated word by word but rather need to be learnt because it is the way how people say it. That's why we can sometimes encounter certain phrase that's correct grammatically but wrong or not suitable in terms of the manner of using it.

In the dictionary Konciza Etimologia Vortaro by André Cherpillod is: farti. G Wohlfahrt «bonfarto, bonstato» ← Fahrt «veturado» ← HE por «trairi». fari. I fare, Oc far, F faire ← L făcĕre ← HE dhe, dha «meti». (...) Je: https://esperanto.stackexchange.com/questions/16/where-does-the-verb-farti-come-from

yes,I think it already includes "esti" and isn't it the same root with "fare well"?