Learn English – Word for writing from memory

I think showing good judgement is exactly what you're describing in "telling good people from bad people", so I would use discernment as the quality.

If you're looking for a more scientific bent, you could use discriminating, which can still be used to mean "exhibiting good selection abilities" even though its alternate meaning of "showing bias" is beginning to take over. It's rarely used when talking about selecting people, for the obvious reason that it can much more easily be confused with its negative alternate meaning.

If you're looking for a more supernatural connotation, you could use perceptive, which has a bit of "unknown origin of the ability" connotation to it due to its use in "extra-sensory perception". Perceptive, however, doesn't limit itself to "telling good people/things from bad" but rather implies an ability to discern hidden depths or meanings regardless of their quality.

"Slacker" has the sense of someone who doesn't do work until compelled to (e.g. By the boss's presence). Where a "shirker" would like to avoid the work entirely, a slacker is perfectly capable of doing something but chooses not to at the moment. Here's one of the definitions from Urban Dictionary: "someone who is very lazy, doesn't do their work until the last minute, and frankly, enjoys it." This doesn't catch exactly what you want, but I don't think you'll find something more specific to the boss coming into the room.