This varies massively from one CM to the next.
If you can get your foot in the door at the higher tier CMs, the professionalism and attention to detail will be exactly as you described. If you can get in contact with an ambitious smaller CM looking to grow with you (their customer), you can also find great attention to detail.
OTOH, some of the smaller CMs in China will gladly tell you whatever you need to hear in order to send the wire transfer, then you'll get back whatever they feel like delivering. That is if you don't get bumped by a higher paying customer taking your spot on their schedule. You might also get great first articles and have great success on the first prototype run, but then they'll take the A team off of your line and have the night shift run it next time with much less attention to detail.