Part of the problem is that the specification of work may not have covered what was actually the problem. If you are in Vancouver and unable to monitor I suggest you grit your teeth and call in a chartered surveyor specialising in Building Surveying: ask him to specify the work required and have it tendered; then certify the work was carried out satisfactorily.
To misquote myself "All short cuts are long cuts"!
There is always scope for misinterpretation.
If my posts can be interpreted in two ways, one that makes you feel angry and one that doesn't, I meant the latter.
Everyday is an opportunity to learn something new.
I'd suspect that 'making good repairs' may be a good solution if you are selling quickly, but will not last the normal expectation of roofing repairs of a couple of decades.
Ubiflex *is* a high quality material (it's expensive enough :-) - 500mmx6m roll is about £100, 6x the cost of flashband) - it is a thick lead replacement product built around an aluminium mesh.
But your surveyor perhaps did his survey from the ground (?).
That perhaps explains the cost of several k. £500-£1000 of that would be for scaffolding, and each element could be a couple of hundred."clear the gutters, cap the chimneys, slate repair and erection and removal of scaffolding at the property to carry out said works"
Perhaps his main error was in not coming back to you at the time to say that the job was bigger than thought.
I think you took the correct route, and hope it turns out OK.
If you are renting out through an agency, they may have a tame (or in-house) Chartered Surveyor for checking the work afterwards.
Refer Mad Regulators to Arkell vs Pressdram.
Never mind getting it repaired - get it re- roofed! That looks disgraceful!
Freedom at the point of zero............