slip something over on (one)
To con, deceive or take advantage of one; to make a fool of or hoodwink one. Hey, these aren't real pearls! Are you trying to slip something over on me? Beware of deals advertised online that sound too good to be true. They're usually just trying to slip something over on you.
slip something over on someone or something
and slip one over on someone or something; slip something over; slip one overto deceive someone. Are you trying to slip something over on me? I think he tried to slip one over on me.