Is the price in the listings statistically reliable? Is the data sufficient to build a model? In my market, there is no car valuation product like KBB, so I'm wondering about building it from the car classifieds data.
Hmm .. Interesting that you say your sector isn't being addressed. Wonder why ... But if so, then that's an opportunity.
I've spent the past 4 years specializing in probably THE hardest market for making accurate appraisals: the domain name industry. For me as an engineer, that has meant crunching numbers. So I'm intimately familiar with the issues involved in making inferences about value from partial list-price and sale-price data.
In fact, I spend much of each day compiling raw data and building database-driven tools to organize and analyze it.
So I don't know the auto industry at all, but I know a thing or 2 about figuring out the value of assets in obscure areas.
Certainly a model can be constructed for extrapolating value from list prices. It only remains to be determined how wide the margin of error would be and what kind of latent bias might exist.
If you'd like my help, just ask.