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?
Herbert - '12 X5 35d / Sapphire Black / Black Perf Nevada / Aluminum trim / ZPP / ZPS / ZCW / ZAV / Apps / 3rd row
Betty - '04 CTS-V / Black Raven / Black Leather & Suede / 6 speed LS6 combo 400 hp & 400 tq
Sterling - '06 Silverado HD / White / Grey Leather / LBZ Duramax - Allison 6 speed combo / Crew Cab Short Bed LT3