To be fair, a lot of "professionals" aren't super competent, even to the point of reading the manuals of things they're installing, and it's difficult to find p

To be fair, a lot of "professionals" aren't super competent, even to the point of reading the manuals of things they're installing, and it's difficult to find people whose work isn't sloppy and half-assed. In these cases the only advantage hiring a contractor brings is their liability if something goes wrong, and their ability to deliver a whole crew on short notice.