They recommend at exchange- but I'm not sure if that is double dipping, to ensure that vendor and buyer both pay insurance for the same thing. Because that's what the insurance companies get.
But you can't guarantee what insurance the vendor has in place (I guess), so perhaps it's worth while doing.
My colleague who lost his house in the ACT fires is obviously happy his house was insured. Adequately. It cost him around $300 pa for a house worth around $400K. AAMI treated him EXTREMELY well (a small plug, but because they deserved it- accomodation was already arranged for him in a fully serviced apartment the day after the fires. MrsW's boss received the same.)
He doesn't like the fact that people who could not afford such a small amount are being compenstaed by bushfire funds, banks, governements and the like. He did get a $10K payment from ANZ bank (another plug!)- but, because he had insurance (even if it did not cover replacement value), he's not eligible for any other aid.
Sorry for getting off the track- it's more to point out the value of insurance, and to suggest that this is one area not to skimp on.
Even to the point of getting revised replacement cost estimates.