Market value of your car is what is the clearing price on ebay of a comparable car.. I would track a few 330s on ebay and autotrader and see where they're selling at. The market is "illiquid" to an extent, though a 330 is pretty common than what I was selling. (Evo 8) Note, on autotrader, if it's a dealer car, you may need to adjust for about $1000 or what you think their profit is.
All in all, you'll get a better price by selling privately. KBB cannot possibily value the cars correctly, b/c it's an "index". My experience has always been that it's overvalued on KBB.