I never go to a bike shop other than to buy something...just bought a frameset from my lbs and they are great people but I believe I do better work...in fact, I know I do.
If you are into the hobby, with modest skills you can teach yourself to build and work on bikes. Any new bike I build or buy or even work on for somebody, I first check the rear hanger for plumb. This is a must as unexplained shifting issues are generally the result of a bent derailleur hanger or one misaligned from the factory which is common. Most new bikes and frames have the derailleur hanger a degree or two off out of plane with the rear wheel.
Below is a pic setting up my new bike. The Park derailleur hanger adjustment tool is a must have if you do your own work.