This is truly horrible advice. Set aside for a moment the complete lack of integrity this approach requires and consider a true story from a couple of years ago:
An enterprising student told Director A and Director B that he was ranking their program #1 at his interviews because he actually did like them both and would be happy at either. Better safe than sorry, right?
Both of the directors were really thrilled, as this student was one of their favorites heading into the interview process.
Director A and B also happen to be good friends going all the way back to podiatry school and shared their newly found good fortune with each other over dinner that evening.
The student was subsequently dropped entirely off the rank list at BOTH programs.
Don't buy in to ethical relativity.