When I tried to get mine valued by the rsoc guy I was told that what they do for modified cars was start at a market value price for the car then if you have spent 10k in mods then they only add a percentage of that to the price, so if a nice condition saph is worth say 7k and you spent 10k on it and you get 10% ( i think that was what the percentage was) then your value of your highly modified car is only 8k

Steve