Depends on the insurer. The approach the Financial Ombudsman advise is to refer to the Guides used in the industry (Glass, CAP etc). They start from a retail transacted figure, then adjust the valuation for mileage, condition, options and enhancements. They also consider the service history and maintenance. They rarely take into consideration examples in the market place, which I believe is wrong. To challenge the value, do not go straight in with a complaint. Make the insurer substantiate the value. Ask them to provide copies of the valuation resource they referred too. Also ask them for a full engineer's version of their Audatex assessment. Any comments relating to condition or options added will be on there. Try to then negotiate with whoever is valuing. If you are not happy, raise a complaint and ask for the value to be reviewed by someone else. If you're still not happy, take it to the Financial Ombudsman Service.