VIP Auto service and Parts Poor or non existant service to customer Windham, Maine

In February 2008 I brought my car into VIP and asked them to diagnose problems that I was having at that time. I gave them a verbal description of the problem and requested that they connect their computer to determine what the causes were and we could go from there. After running a computer check ($75 charge) they informed me that there were 29 error codes and my problem was being caused by either a plugged fuel filter or a clogged cat converter. They suggested that we should change the fuel filter because that was the cheapest way to determine which was causing the problem. The fuel filter change didn't help (another $73 and change) and I was given a quote of over $700 for the cat change. I then told them that I would have to wait so I could come up with the money, paid the $148 and change and left. I then took it to another mechanic who put it on his computer and told me that I only had 2 error codes (cooling fan relay, and heated O2 sensor) we replaced a fuse for the cooling fan and reset the codes and the check engine light went out and stayed out. I then put two cans of dry gas into the tank and all was fine from then on.
My complaint was that why did they charge me $75 for a computer diagnostic and then have to guess what was wrong and still not know. If I had blindly followed their lead I would have spent almost a thousand dollars and still not solved the problem. Thank god for second opinions from honest informed technicians.