Appearances/Looks can be deceptive/deceiving.
MEANING
people or things are not always the way they look
EXAMPLE SENTENCES:
The pupils looked angelic – but appearances can be deceptive.
He appears to be happy, but appearances can be deceptive/deceiving.
Appearances can be deceptive.
Looks can be deceptive.
Appearances can be very deceiving. [ =deceptive]
Gwen’s students may look angelic, but appearances can be deceptive.