Apart from 'complete failure' within reasonable perameters, everything is salvageable.
The reason u'll get conflicting advic from tradesman will dependan on several factors.
It's in our nature to judge by our own
standards, therefore automatically u'll have a difference of opinion from any potential fitter if contracted to carry out remedials to the project.
What's acceptable to one fitter may not be to another, we see that on here all the time!
Secondly it'll depend whether they can actually be bothered to patch and repair as opposed to a complete rip out, at the end of the day NO tradesman relishes the job of putting someone else's work right, paid well or not.
It's an arse of a job!
Then of course it's dependant on the level of overall finish u require, has that changed since u've been on here?
Is what was acceptable to u 6 months ago, acceptable now?
Probably not!
So any inspection/report can only be based on a 'fit for purpose' basis.
Which means as long as it falls within BS 5385 it's 'fit for purpose'
Aesthetics won't come in to it.
So I believe your best way forward is as Paul advised, and that's with an independent inspection by someone who's recognised by the courts.
The court may not recognise a random tradesman as an expert witness, that could well be judge dependant.
I could go on, ( as members can testify! Hehe
) but hopefully I've made point.
But it is only MY opinion.