One of my co-workers was tasked with monitoring the implementation of on-board Wi-Fi in our regional jets; the subcontractor started zooming through the job, he stopped them, saying "hey, this isn't what the engineers drew."
They replied that "this is the way we did it for airlines A, B, C... it's good."
He said, "no. Do it according to the drawings." Near riot. They threatened to strike, a few people were fired, they tried to call breach of contract, but finally knuckled down and did as he told them.
Six months or so later, ours was the only regional with FAA approved Wi-Fi on-board; all the others had to shut down, tear everything out and reinstall.
The moral is, subs are going to cut as many corners as you let them, and if you don't watch their every move, you are likely going to pay for your inattention...