[gearhead]

Most are OK from the factory, but the field tech will use way too much bluing to check it. That really doesn't tell you much except you used too much bluing. I was trained to use a very light application of bluing, then transfer that with clear Scotch tape to a pure white piece of paper.
Some vendors were pretty good at slopping a lot of bluing on a taper and asking me...looks good huh? No, it doesn't.
Nothing like having a taper on the coupling on a 80,000HP turbine getting eaten alive and bringing a major Gulf Coast ethylene plant to a halt. "Force Majuer" declared.