If I see any Yaksha (Demi God) in Hindu philosophy, how do I know if this Yaksha is good or bad? Any documented source is good.?

Question

I have seen some spirit (as I perceived), Female person as well as Male person at different times, after some research, I am thinking they are Yaksha, Then why they are showing to me? is they are good or bad? if they are bad, then what are the remedies?