So you don't know much about cars? You are alone. Is it a coincidence? Does knowing less about cars make visiting a mechanic more painful?
It seems that people that have little mechanical ability, have a tendency to have more wrong with their vehicles. I suspect it’s because the car has an issue with the person driving it, but I could be mistaken. That happened once, long time ago. I was mistaken. Didn't care for it much so I decided to stop.
Now there may be plausible explanations for this. People with less mechanical ability may not recognize symptoms as quickly. They may not know what maintenance needs done, or they may let things wear further then they should, which in turn causes other things to wear out resulting in a higher repair bill.
But, I suspect some of this may be because some mechanics use their own knowledge to their advantage. Suggesting repairs that may not be necessary at that time. And without some knowledge, non-mechanically inclined people have little recourse other then to make the suggested repairs.
How do you avoid these situations? Take someone with you that has some mechanical knowledge. Get a second or third opinion. Let someone else take your car to the mechanic. Always drive cars that have a warranty on them. Or you can ride a bicycle. All are good options, yet some more expensive then others.
It is important to have someone that you trust be the person working on your car. It’s also important to not be taken advantage of. Always get a prioritized list of repairs, let someone else drive your car and see if they notice any symptoms you've missed. And put a bicycle in the trunk just in case you're out of cell range when something you didn't notice fails.