I don't think any of the "guides" are accurate, they (guides) take into account BJ auctions/etc...tis why the "guy down the road" wno't sell his rusted out '39 for less that 25K, because "just seen one sell for...."
For me, I look at Ebay for pricing, evaluate sold auctions...figuring the majority are bought sight unseen, you can add a bit-assuming the vehicle in question is the same/similar shape- if you're selling/buying locally, well, assuming a "nice car" and not a project car, seems Ebay has the right buyers for project/needs work/etc vehicles.
Just how I "value" many things when looking to sell or buy.