Overall my experience at AA has been good too. Good prices, two stores nearby, easy online ordering. I had one case where I couldn't believe what they did. I had an alternator that was about 2 years old, still under their warranty. They didn't have that same brand alternator anymore, so I was expecting them to offer me a similar one. Instead they proceeded to refund me the full purchase price of the original, then sell me a new one that cost $40 less. IDK of any other business that would have handled it that way, I sure would not have. I came out with a new alternator and $40.
Their free tool rental has come in very handy a few times too. I've borrowed tools sometimes when I couldn't even buy a part from them for that repair, because they don't carry it. They could offer a code scanner as part of the free rental plan.
IDK how fancy a tester they had or what it costs, but labor cost would add up too. They have to pay someone to go do it. And then I'm sure a lot of people proceed to ask all kinds of questions as to what it all means, what to replace, etc that could tie them up for 20 mins. Thinking about it, that part, responding to all the questions, is probably what gets them in trouble, with some customers blaming them. The code reader doesn't tell you what to change, what to fix, it only tells you what codes it sees. Even for mechanics, it then comes down to experience, further testing, an process of elimination. I''m sure there are plenty of people out there that don't understand that.