If you don't trust the expert then why are you asking them to fix your stuff? It's a weird idea that you'd want an idiot to do what you say because you know better.
If they're asking the mechanic to do X and they understand the mechanic is just doing X and NOT venturing to fix your problem. I guess that is fine.
I agree though it sets up a weird dynamic where folks might come back to the expert and complain a problem isn't fixed, but that's not what they asked for / they broke the typical expert and customer dynamic.
In my experience the best thing is to then convince the expert you are right, using your own expertise.
If your mechanic is too stupid to recognize the problem after you explain it then you don't have a mechanic, the set of hands you are directing is basically unskilled labor.
