Among other oversights, they somehow forgot to pull two new electric lines (which we had contracted and paid for) into our kitchen before the walls were sealed back up and painted during a renovation.
This required additional demo after we had already moved in and had the place cleaned. It was only discovered during an electrical inspection, and could have easily been missed altogether.
They also omitted a new light switch and outlets which is a real pain now the reno is over. We paid a premium price for them and when we complained to the owner, he basically just shrugged.
The new lines were added but at a great cost and inconvenience. The outlets and light switch were never installed (we ended up getting one with RF transmitter to avoid more construction).