As far as "blue book" or other sites that "value" used vehicles, I take them with a grain of salt. Ever since the recession of '08 the used vehicle market has been very active and decent used vehicles can typically command much more than "blue book" in most markets.
"Blue Book" might make sense if you are talking about cars that are interchangeable appliances like a Corolla or an Impala or an Accord - IOW, a vehicle that people only get because they need something with 4 wheels and a motor to get them around town. Anything that is in demand from an "enthusiast" market - which includes any kind of "sporty" car as well as trucks and SUVs - is almost always going to sell for higher than "blue book."
In fact, when I owned my 4runner, I would get flyers from a dealer every few months offering to buy my 4runner for 100% of blue book value, cash in hand! My wife also got the same offer on her '06 Grand Vitara. These dealers wouldn't be buying these for over blue book if they weren't selling them for way over blue book. (If I was a cynical person I might think that car dealers are pressuring the likes of KBB and Edmunds to undervalue used cars just so they could make these kind of "we'll pay you over blue book value!" offers.)
FWIW I paid $10.5k for an 04 Suburban LT with 136k on it just last December. Did I overpay? Probably, especially considering that I did find some rust underneath (though most of that is surface rust.) OTOH, the truck had the exact options I wanted (leather, bench 2nd row, no autoride and no sunroof) and is loaded with just about every other option except for navigation and rear seat DVD entertainment (neither of which I need.) It has the G80 rear axle, towing package, aux transmission cooler, power folding mirrors, etc, so it was worth it to me to have exactly what I wanted when I needed it. There were trucks that were less expensive but either they had over 150k miles, or they were otherwise unsuitable for me (I found a lot of black trucks - I live in a sunny part of the country and no way in hell am I getting a black or dark blue Suburban.)
