How do you find out the depreciation of a car that was involved in an accident earlier?

Was it repaired to pre-accident condition? If so then really no depreciation right? There is a lot going on now with respect to 'demished value' claims after a loss. Lots of things come to play, exactly what was damaged, and how the repair was completed, etc. Check with dealers in your area, re: what is this worth, with no accidents and what if there are some (accidents).