Khan,
Dealers stopped using the NADA and KBB decades ago. The data required dealers submit frequent reports and many didn't out of laziness amd exp[ense so it was an inaccurate data set. Were it not for the Internet and them pandering to the so-called "educated consumers", both would be long gone. Hearst Publications publishes a regional auction guide called the Black Book. It is a dealer-only printed publication but there are often links posted by credit unions that you can get to, here is one:
http://www.blackbookusa.com/bb/produ...d=cudirect.com
The data comes directly from recent auction sales and represents what vehicles are actually selling for at wholesale, categorized by condition. Note, your car is only extra-clean if it has zero miles, everything else falls in one of the 3 remaining categories, most likely average. Once you have a general idea what the car is worth at wholesale, you can make some offers that aren't quite so insulting. In this depressed economy, most dealers would like to get at least a $1000 profit, and on fast-moving cars maybe more. On a $20K car that's 5%, which is only fair.
As for trade-ins, dealers don't approach this from a risk management perspective, the auction is their insurance policy. When they bid a car they have already decided whether they plan to take it to auction for a quick $100-300 profit, or keep it and try and sell it for a larger $1000-1500 profit. And even if they DON'T run to the auction immediately, they will bid it safely to be able to do that if it sits unsold on their lot for 45 days.
Bartruff1 is right...eBay is generally a reflection of what the market price is, because its national and its real time. But people will and do pay more locally for the peace of mind and convenience of not having to have a car shipped across the country.