Hi Pico - This is Duane Benson from Screaming Circuits chiming in.
What's really important, is matching your needs to the strengths of the assembly shop, and making sure your data is solid. Good shops will catch most data irregularities, but no one can build anything better than the data they get. Even from the best folks, about 70% of what we see has some data that needs to be corrected or clarified.
Here's a blog post that gives some advice on making the transition from hand build to outsourced assembly: blog.screamingcircuits.com/2016/06/from-hand-assembly-to-robotic-assembly.html. Most of what's in our blog is advice to engineers based on traps we see in our operations.
It's really about tradeoffs: time vs. money, expertise vs. money, and the amount of work you need to put in vs. money.
We do a lot of high-end work, so, as has been noted, our fast turns can seem pretty expensive if you're used to hand building. We also have a service we call Short-Run Production that has a few more requirements, but is much more competitively priced in the hundred plus volumes. You can get a quote online without having to register or talk to anyone.
Duane Benson