play someone false

play (one) false

old-fashioned To deceive someone; to cheat or swindle someone. I insisted that they offer something as a collateral before we entered the deal, lest they be playing us false with their offer. The rogue had been playing the old lady false for nearly a year, preying on her trusting nature to bilk her out of her fortune.
See also: false, play

play someone false

prove treacherous or deceitful towards someone; let someone down.
See also: false, play, someone