I thought the entire reason 'agreed valuations' existed was to close the loophole between the stated value by the insurance proposer, and the inevitible arguing that occurs come crunch time between the insurer and the insured.
I have had agreed valutations, which were provided by way of an additional charge, and were only verified by way of a document once the insurer/underwriter had seen evidence of the vehicle and agreed to it's valuation. They won't agree to an unrealistic valuation, hence why they require evidence (photos, receipts - sometimes an inspection in person) before accepting the valuation and the initial figure stated by the proposer isn't always agreed to.
I think Mudster must be referring to when people take out regular insurance policies, and overstate the value of their vehicle. This value volunteered is in no way agreed to or verified, and the payout after a total loss will be of market value only - which can obviously be of greater issue when dealing with specialist/classic/collectable cars. I think he is correct though when he says - on regular policies, the value stated is only used for calculation of the policy premium.
Will