When I bought my new car a long time ago, I notice the trans fluid was a little high so I had them drain some of it out. This was when I knew nothing about car. They did something and I drove my car home. A few days latter, I noticed the fluid was leaking. It wasn't much leak but enough to be alarm. I drove back to the dealer and they said the mechanic broke a valve and rod when trying to adjust the fluid level for me using a special machine that they just got. They said they will take care of it and this is a rare thing that something is not done right and the fault is on the machine that is too new for people to be familiar with. So they did something again and gave me the bill. I was like: The fluid adjustment was done under warranty and you guys screw up, so why charge me. The a-hole named Johnny gave all kind of excuse and the conclusion was that they had to do a fluid flush as the vehicle had 30k mile so they can charge me since it is a maintenance item in their book. It was late so I paid it.
The next day I call the manager and got shop credit.
So the point is that dealership can't get thing right too. Like 6 months later I started helping the family business and help change the transmission fluid on our delivery vehicle. That was when I found out the process and system is just like changing oil, with no special valve or rod to break. Basically, the mechanic just didn't tight the drain nut correctly so the fluid leaked. Simple. How can a mechanic not tighten the nut correctly is beyond me. They should have come clean and win my trust at that time. From that point on, I haven't taken anything to any shop for maintenance. I just buy book, use sites like this one, and ask friends to learn how to do it myself.