Unless you have a license, auction prices are not representative of what the OP is looking for in terms of a reasonable price he will pay for a used car. It may be what the dealer will give you on a trade, but it is not what Joe X will be able to buy the car for.
Maybe that's what you meant by "apparise a luxury car 3-5k back of wholesale book"? I didn't understand what you meant by that. Are you saying take auction prices and add $3-5k?
Rover - 2013 Holden Commodore SV6 Sedan
Clark - 2013 Holden Commodore Sport SV6 Wagon