Is it ok to play dumb?

At times, I play dumb.
I pretend to know less than I actually do.

And... I wonder... is it fair to do so?

Should I, if aware of an issue or the entire narrative, leave gaps for others to fill in order to -

a) give them the opportunity to raise an issue on their timeframe (within reason)
b) hear their side of the story
c) allow them space to only share what they're comfortable with me knowing
d) have a subtle test as to how much they want me to know and how much they want to hide.

Is it ethical for me to dangle enough rope before people in order for them, potentially, to hang themselves?

Or, should I always fess up?

Hmmmm