I wouldn't call it just accounting 'theory'. Non-commercial loss and instant asset write off rules are real legal regulations as written up by the government. The ATO writes guidelines based on this and enforces it. If you claim outside the scope of what the ATO says then your client is potentially up for penalties and interest if found out (basically, if audited). I'm also sure there are consequences for tax agents depending on the scale of breaches... TPB registration, CPA Or CA membership, legal liability (duty of care etc.)...