I have to disagree to some extent PJ2, I've sat the 5 day DG course and 2 day refresher every 2 years, and most people to my knowledge who do DG checks whether a loadie, handler or airline do a pretty good job. I'd suggest those doing it day in day out would spot errors quicker than a F/C sat with a DG manual.
As to incomplete NOTOCs, that is unforgivable, as is missing a CAO item (they have different PIs for one)
Having also dealt with skippers who know better than the manual (a tiny minority, but they are out there) I'd still trust well trained, well paid, checkers with reputable companies to do everything correctly. Including a skipper who would not accept than compressed oxygen was not RFG (flammable gas).
It's the shippers I don't trust, especially those on a "budget".