I can understand your fear of mechanics making a mess of the service, as the DSG is a very expensive part and it could easily be messed up by someone just not taking the care you would like them too.
The only real way for you to get peace is to go to someone whom has been recommended to you personally by someone you trust.
I got my first service done by a small garage called Votex in Congleton. There is a old fella in their polishing cars for customers who are even older than he is. It doesn't look anything special but they are rushed off their feet every time i go, and i can just tell by looking the guy in the eye that i can trust him to treat my car the way i expect him too.
The first time i went their it was to get my coilover's fitted, my car had just been detailed and was looking better than new. When i went to pick the car up the first thing he did was take me to a tiny scratch on the rear wheel and he said, i would like to point this out to you we did not do this. I knew about the scratch before hand it was just a graze from a twig or something, but this showed me that he has very high standards and could tell just by looking at the car what it meant to me.
I will be taking my car to them for the DSG service when it is ready, and i wont worry about it one bit.
Sorry for the waffle but go to someone highly recommended or take a leap of faith.