Pretty much all I do is diesel repair and I've been doing for a long time. I've had trucks towed in from the dealer with an estimate of well over 10k to fix the no-start, the dealer wants to do a whole fuel system.
The dealer usually tells them they found metal shavings in the fuel filter and they need a complete fuel system. I'll pull the filter and won't find any metal shavings, what the real problem has been is an injector is bad and is dumping the rail pressure and the pump can't keep up, a common rail needs 5000psi to start, so if it can't hold the pressure (because of the bad injector leaking) it won't make the 5000psi needed to start.
So far I've seen about 10 trucks that only needed injectors and not the whole fuel system, I have yet to see a confirmed bad CP3/CP4 pump, I'm sure they are out there but I think most are misdiagnosed.