Here's the catch: Let's say you have a problem with your car. You think you know what it is (or in your case, you read the code). You tell the mechanic "I want you to fix/replace X", based on what you think it is. They give you a price, you say OK, they perform the repair, you pay them, and drive off. But the problem is still there! Now what? You can't get mad at them, or ask for your money back, since they just did what you told them.
Your solution is to find a mechanic who WON'T charge you, just to figure out what is wrong. And don't say it's not possible, since it's the only kind of mechanic I've gone to my whole life. A good mechanic is very valuable.