I Don't Know Nothing
The dealers generally do diagnosing of issues or problems with their software and usually do not tune. They may do a reflash on the tune to fix or update certain issues the factory approves, but that is not what is referred to as tuning.
Carlos
Wanting the same as you and after doing some research I chose HP Tuners and I have been happy with the product and what it allows one to do.
You should understand there is a learning curve and courses like the Tuning School or Calibrated Success are worthwhile because they teach you about the software and tuning. Experience and education are inter-related and while it is not free or cheap to get these can save the newbie a lot of frustration, and time in the long run. My experience with dealers has not been a pleasant one when I needed service work in the past, so considering those things I find self education and tools worthwhile investments.

