Wow that's a beautiful website, Karl!

 

What you experience is probably a seasonal thing, ie pple tend to sell cars with a higher $ now than later in the year.

I actually scrape ebay, cars, autotrader data on a weekly basis for my own analytics. Hoping to build regression models for various makes. Thing is there are lot of outliers for AMV8, ie dealers/private who value their cars based on very subjective and irrelevant metrics. By the time I weed them out, the data set is too small to do anything, hence the need for historical data (yes adjustments to made much like HPI).