I guess the problem there is that he knows that he should have done it in the first place. That's just shoddy. Like when someone on a recent video I saw had put grommets in only one of the 4 board knockouts. He knew he had to do it otherwise he wouldn't have done the first one, but he's seen the other three and thought 'can't be arsed'. Very poor.
As for the plumber, most of his work seems alright to me. There is a tendancy of other tradesmen especially online to rip the work of others to shreds when in reality there's nothing wrong with it.
I've seen literally perfect work on youtube by some carpenters get some joey in the comments who just has to complain and say how poor it is and how they can do it better. I think it's just the need by some to feel knowledgeable and important. At the end of the day some are out grafting, earning, and some are sat criticising behind keyboards.