The only reason dealers don't have the same problems with repairs and can charge a slightly higher price is because they are specialty shops, only dealing with repairs to their brand automobiles.
There are way too many TSBs (Technical Service Bulletins) out regarding each brand and model for a General Practitioner to stay up-to-date. They are already available to them through the manufacturer, and if they don't know where to get it, they could call the local dealership to get that info as well. It's not like dealerships are so stingy as to horde all the manufacturer's information away from you.
For example, the computer gives the code showing that a sensor is malfunctioning, but the TSB from last week says that it's not the sensor, it's a ground short in the wiring. So the General practitioner just replaced the sensor thinking he is done, but the problem will remain until that wiring is fixed/replaced. It's not the manufacturer's fault, as they announced the real problem. That would be the General Practitioner's fault for not knowing the TSB. Don't get me wrong, dealerships are known to have this happen as well, but at a lower frequency.
I guess what I'm getting at is that General practitioners are ok when you know what the problem is, but even with this legislation, if the mechanic you take your car to isn't up to date with all the brands' and models' TSBs, there is something that they will likely miss. Then when you take it to a dealership to fix what the other mechanic couldn't fix, you basically just paid twice for what should have been one repair.
Just like a Doctor, you wouldn't see your general practice doctor to fix your toothache, or to do reconstructive surgery.
This bill will likely do nothing to change prices or service in Massachusetts.