The major problem is if you don't understand the job and how long it takes and what's involved it's easy to get screwed on price. I've had to bring in some outside guys here and there for stuff that was beyond me - or I didn't feel like taking on - but I still know what's involved - time and materials - that I can ballpark a job price pretty accurately. And that's why it never hurts to get a ton of quotes. To tape and mud my workshop - which I do know how to do but absolutely hate doing - it was a day's work plus some material. I had some guys quote as high as $1500 - for which I laughed at them. Guy I hired came in at $300 which was fair. $30 an hour for his time, plus his incidentals like gas, etc and materials is exactly what it should cost.
You can always rely on a larger, more established contractor but you're going to pay out the ass for it and it's not always worth it. My old electrician expanded last year finally making the move to build a real business, and as such his rates skyrocketed and I won't be using him anymore.
"If you're going through Hell...keep going."
- Winston Churchill