The most reliable way for the insurer to validate the value of the item is by providing a receipt for the purchase of the item. If the receipt is not available, the insurer can check the market value of the item in question. In case of repair, the insurer would need a cost proposal directly from the repairer, which would have to be approved before proceeding with the repair. In the case of theft, you would need to see a copy of the police report.