Since most claimants get their vehicles appraised by CarMax after a loss, the CarMax appraisal report would only be quantifying the post-repair cash value of the vehicle.
Most claimants deduct this post-repair CarMax amount from NADA retail or other online valuation sources when computing DV on their own; this is not accurate as we don’t know what CarMax would have paid for this vehicle before the accident.
Since CarMax only represents 5% of the used car market it is therefore hardly an indicator of the entire automotive marketplace and its buying habits.
Additionally, CarMax only retails non-damaged vehicles and will be extremely prejudiced against vehicles involved in car accidents and would offer below market value for them as they do not meet its ideal inventory mix. This is generally not duplicated across other dealers in the market as CarMax operates its own wholesale auction and makes a profit of its non-retail inventory.
To properly quantify Diminished Value , an independent source needs to assess the vehicle’s value before and after the loss, a source that has no financial interest in acquiring said vehicle.