G-Tech Auto Service

I have a 2004 Mazda6 which ran rough when I bought it. I took it to G-​tech for them to diagnose and fix. They did extensive work on it (about half of what I paid for the car), and it ran somewhat better but still had the same symptoms. I took it back to them a few times after the initial repair and they told me it was fine. The car continued to run rough, and finally got to the point where it was dying and not wanting to run. I took it back to them (big mistake!), and they did more work, telling me that it was an unrelated issue. There was a slight improvement, but it continues to run rough, hesitate when accelerating, and smokes. I’ve since found out from another mechanic that there was an oil seal leaking that had a very shoddy repair job done on it.
They seem friendly enough at G-​Tech, but my impression is that they are not very knowledgeable when it comes to any kind of engine work, and that they are eager to charge customers whatever they can, whether or not the issue gets fixed.