What is a market value insurance policy?

What is market value insurance policy in Australia for car and home, it is policy where insurer pays market value at time of loss, not agreed value, with market value being what car or building would sell for just before loss, costing cheaper premium 10% to 20% less than agreed value. For car insurance, market value policy pays market value $18K for car if total loss, based on comparable sales and RedBook, versus agreed value $20K fixed, with premium $800 per year for market value versus $900 for agreed value for $20K car, saving $100, but payout lower $2K less. For example, car bought $20K, market value after 2 years $16K, if total loss, market value policy pays $16K, agreed value policy pays $20K if agreed $20K. For home building, market value rarely used, as building insurance uses sum insured rebuild cost $500K, not market value including land. Market value policy cheaper premium 10% to 20% less, but risk of underinsurance as market value may be less than replacement cost $500K rebuild versus market $400K if land low, so you get less. So market value insurance policy pays market value at time of loss based on comparable sales $18K for car, cheaper premium $800 versus $900 agreed value, but payout lower and may not cover replacement $20K, with agreed value better for certainty $20K fixed payout, market value cheaper but risk of lower payout.