[hobs]

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.

[duxup]

How do you know you're right if you haven't fixed it?

That seems like a way to just be a stuck in the mud and wrong the whole time.

[hobs]

exclude the impossible and what is left however improbable must be the truth

[duxup]

If we're still talking about an amateur doing it, isn't their understanding of the possibilities petty limited?