In my opinion, actually caring about the result makes all the difference.
I finished my 900 sqft basement including electrical. Everything was perfect, and the inspector was kind of blown away. The reason was because I took 2 years to do the whole basement, and if I spent a weekend doing just one circuit, that was fine. A pro would never be able to spend that much time.
The quality of the work though… it's not that I could do better, it's that I've done better at specific tasks e.g. when they R&R'd a ceiling fixture I'd installed. We would've parted ways a long time ago if they'd done things right the first time. Instead I'm slowly going over their work to make sure I don't get screwed even more.