I had resolved to go to the dealership for car troubles after my (then) car needed a new catalytic converter. In an attempt to save money, we had a friend/mechanic replace it. I don't recall all the picky details, but the catalytic converter that was installed did not work with the O2 sensors, so the check engine light was on and I couldn't pass the yearly emissions inspection with the engine light. The dealership fixed it up right nice. It was more expensive to fix at the dealership, but that car is still running even after I transferred it to my son at 220k miles.