Some kinds of spirits can and do lie.
Some, including the Fair Folk, can’t or won’t.
*However*
~ this is the important part here ~
Just because a being is utterly truthful doesn’t mean they can’t deceive you. Never assume that something telling you only the truth is the same as that spirit being honest with you.
Telling the truth is saying something that is factually true.
Honest is being free of deceit and sincere.
*These* *are* *not* *the* *same* *things*