You'd be surprised what you find on Craigslist.org. Of course there is a lot of overpriced items, but if you are patient, you'll find others like yourself looking at trading good quality for reasonable prices. As with any public trading websites, make sure you use precautions when meeting others, and know your product before inquiring. If you work it smart, it'll definately pay off.
Another vote for KEH in Atlanta. Their ratings are indeed conservative. My brother purchased a "Bargain" rated lens that looked very little used. You might pay slightly more than some of the auction sites, but it's way safer. KEH has a liberal money back guarantee.