I have to defend the dealerships, not because I spent so many years there, but because I believe they are right. If you want a FREE scan then go to your local auto parts store like AutoZone and get a free scan. If you want a technician to scan your vehicle with a proprietary scanner for your specific vehicle, and get an estimate for repair, go to the dealer. Many times technicians know of ECM updates or TSBs (Technical Service Bulletins) from the manufacturer that can fix your problem. You basically get what you pay for. Free gets you a code, that may or may not be your problem. Pay $75 and get a technician to diagnosis your vehicle with an estimate of repair. Most dealerships will apply the cost of the diagnostic to the repair. It is NOT called a refund. I am very pro dealerships in things like this. Having seen too many independent shops misdiagnose by using a cheap scanner or repairing something that the dealerships would have repaired for free because it was a recall.
This is 100% true.
You wouldn't have the pharmacy assistant take your temperature and vital signs, then go to the doctor and expect him to remove your appendix without first verifying that was the problem, would you? Because that's about what having Autozone read the codes amounts to.
An O2 reading lean may be a bad O2 sensor.....or it might mean your engine is actually running lean.
As far as the "refunding of the diagnostic".....there is no such thing. You expect them to diagnose the car, then not charge you for it, and just charge you for installing whatever part it is? Right.
I've seen it termed different ways...."the diag charge goes towards the cost of the repair"...either way, you do NOT get it back. It simply is included in the charge of the repair they quote you, as it should be.
Now, as to the shop going over the car's dents and dings before she left it: That's because they've been burned by a-holes who have dropped their cars off that they knew had damage, then accused the dealer of causing it afterwards. So they now make the customer acknowledge whatever's wrong with the vehicle to prevent this. If customers weren't generally dishonest and less trustworthy than mechanics AND salesmen, this wouldn't be necessary...but the fact is, customers suck. They lie, and they are constantly trying to get something for less or even nothing. Work for a dealership and you'll see it over and over and over.
Finally, I'll say this: Yes, sometimes whatever's throwing the code is the issue, and needs to be replaced. But sometimes, it's not. In fact, at least 50% of the time, it's not. Or there's another issue that's being masked by the first code that pops up.
So while you can certainly find cases of where a dealership mechanic misdiagnosed a car and it was later fixed by an independent, you will find FAR more cases where it was the other way around. And even more cases of where someone has already spent a load on sensors and tune up parts based on parts monkey's "diagnostics", then took it to the dealer and had the problem properly diagnosed.
Dealerships aren't infallible, but the numbers are on their side, pretty overwhelmingly.