1. You would
need to seek expert valuation opinion to comply with tax law obligations to determine the value. This is explained in the ATO document I uploaded. The taxpayer who doesn't self-assess may need to then seek expert opinion. That cost would be deductible. BTW The 1970 property example is pre-CGT so its a no-brainer. No valuation is needed.
2. Remember its self assessment. If they disagreed with you they might choose another value and amend. You then have to prove they were wrong. So lets return to point 1.
3. Cost applies if you are the owner. A QS wont increase any deduction in this example other than maximising the deduction claim. All CGT costs after (its an IP) add to that value as the first element of the cost base.
All these issues are taxpayers self-assessment problems and would likely affect final CGT being overpaid perhaps. Good reason to keep diligent CGT records for all properties. Its the tax deduction that is often overlooked.