This girl at work, I do not know how she does it but she keeps a STRAIGHT FACE when?

she is telling people something. She is s Supervisor. A lot of times she has to say NO with a reason to very angry people.....The whole time just looks at the person with a STRAIGHT face. Did she PRACTICE that? or is that how she is??? (I have to hand it to her...she is superb). I have heard her say to customers.."that is policy sir...and the person keeps complaining. She politely tells them AGAIN.."that is our policy sir."...and just looks at them with a STRAIGHT face, no emotion...and the person is STILL complaining. She says.."Sir, that is our policy>"..and slowly walks away!! Any opinions??? She is super!!!