For clarity in this hypothetical situation Bob the independent mechanic has nothing to do with Ford nor have you taken it to Ford to then be subcontracted out to Bob.
It could have been complaining about the work done by Bob on your Fiesta to VW in my example and it’s still the same outcome. They would be well take it up with Bob. 
Bob then goes look I fully explained to you that it’s unlikely that replacing the part would fix the issue but you said proceed anyway.
You reply with, but the person I’ve just met said I should go ahead with it.
Yeah it’s a loose analogy. The key take away is 