still looking for a good definition of "successfully typing"
That was my question too. You can compare to their self-assessment, but most people don't look further than the (often inaccurate) online tests or best case, descriptions. Even if they get an official assessment (and who here has?), I don't think those are infallible either. It depends how well you know yourself as well as how easily you fall into one of the boxes.
I could wager a guess as to which type likes to think they know other people the best (), but I'm not sure you can accurately measure whether you are actually getting the right impression or not..
I think I'm pretty good at reading people, but pretty bad at placing them in preset categories, definitions and applications of which are contradictory from one person and source to the next. If mbti were objective, that would be one thing, but it's not, so I'm the first to admit I have no idea how to determine what type to place most people in. I have no idea which system to use, as there's little solidity and consistency even between those who consider themselves experts.
Also, although some people are pretty strong in one or even all categories (whether dichotomy or cog function), I think many waffle in grayer zones where they don't have crystal clear preferences in one or more. At least in the sense preference/mbti is talked about and practiced on this forum. And in those cases, I question the need to even bother with placement in one set type. What purpose would that achieve in the end?
"...On and on and on and on he strode, far out over the sands, singing wildly to the sea, crying to greet the advent of the life that had cried to him." - James Joyce
A weak point of "sf"s is objective problem solving. SFs can execute an a problem if some one tells them how or mimic others behavior, but they lack in creative thinking and the objective problem solving that is necessary to understand what goes through anothers head when you are and intoverted SF and not as open to new information as p types, theoretically putting isfj's at a disadvantage. side note: i think entps may be inherently better at reading people and they are opposite to isfjs.