Earlier quoted context omitted.
Perhaps the fake PIN would only show a preset of money in the account (and still call the cops)? If the robber didn't know the victim, they might buy it.
I think that's the far more sensible option. Sure, they might get more violent and say 'use the real pin', but honestly, how are they going to know that there isn't only 67.87 in the bank?
All sorts of stuff is going through your head like "should I use the duress PIN?" , "can I remember the duress PIN?" , "will they know if I use it?" , "how could they know?" , "What if they somehow DO know, is it worth the risk?"