Your whole premise is based on the home owner not accepting the dwelling without fault. How would they know? And that is the core issue that I'm highlighting.
The home owners must obtain assist from a professional in the field to ensure that their home is built in accordance with the rules. Unfortunately, most don't bother and then they end up in QCAT or VCAT or NCAT.
My whole post is to assist and highlight this issue.
Without giving anything away, if I was you i would accept what Marcs is saying as he knows what he is talking about and has expressed his opinion which is accurate far better than my feeble attempt.