Can a diagnostic machine at garage? ?

My subaru went on a diagnostic machine and found it needed crank shaft sensor (which I already knew but needed 2nd opinion). A friend has just been told by RAC man that she will need one but the bloke at her garage said that I was obviously lying about the diagnostic machine because there's no way it would pick that up. I now feel crap for being taken in in the 1st place or is this friends mechanic lying?? PLease help