3 traps should notice when repairing your car

What is really a headache for the comprehensive car owners? It is that you are fooled when repairing your car is a 4S shop, what's worse, you don't really get it but to compliment good maintenance technology. And now, it is a prevailing trend that most car owners try to do it themselves by using some reliable tools, such as auto diagnostic tools.
What's more, owing some kinds of basic tools will, to a great extent, save you much trouble when emergency happen. And we cannot expect a tool for solving all problems, but at least, we can avoid that whatever happened in your car all need repairing in the garage.
Why the idea occurred to me? It happened to me and let me felt so angry. What happened to me can be simply classified into 3 traps.
1. "High" hourly wage
Previously, I drove my car to a local 4S shop owing to some of small problems caused by neglect of maintenance. It charged me very high fee as I expected before, much importance of all, I did not feel any great change in my car. Finally, I ask for a maintenance record, but they cannot issue. Although it was charged on the basis of hourly wage, you have right to refuse payment for the reason listed above.
2. "Misdiagnosis"--- get more accessories replaced
"Misdiagnosis" is a common thing that the staff tries every measure to get your part replaced regardless of bad ones or new ones. You must pay more attention to their operation when repairing.
3. Substitute bad for good
One day, I drove my car to a 4S shop for adding engine oil. I forgot to bring something at the supermarket that I bought before. But when I came back, I found that the staff replaced my oil with bad one and charged me high fee.
There only several traps I found, but only exist more, so to be careful when repairing. If possible, you can try to use car diagnostic tool. And I know that a obd2 shop provides a full series of car related tools, which I bought for many times and turned out to be great.