I'm not assuming you can obi, but surely only an idiot would sign off work as his own without checking/verifying it all first. If there's some of the system they cannot check and they're doubtful of, then they shouldn't sign it. If they do...the're an idiot! Maybe its a small enough job that they can check it out and certify it with confidence.
That's seems like common sense to me. A corgi guy would be risking a lot if he signed off work that he couldn't verify and then something subsequently went wrong with it. I mentioned professional suiide in an earlier post.
Is it a measure of a non-corgi fitters physical incompetence that he has to get a corgi fitter to sign off his work?
Or is it a measure of moral incompetence on the part of the corgi fitter who DOES sign off on someones elses work?
Plumbing paradox
In essence I agree with what you are saying Kjacko, At least someone is signing it off I suppose!
However, my previous point was how can you tell if a tradesman, in this case a plumber, who hasn't passed his ACS assessments is competent? By their very nature exams are, or at least should be a test of competence.
In the real world when a non registered fitter/plumber installs a system, it is most likely that the system will be commissioned and running prior to it being signed off.