A:Believe it or not, I actually use Craigslist quite a bit, too. That's mainly a function of how many people are on the site, and in my area there's a great selection. One example is this slightly used Osprey pack for $175. It's been out of production for for three years, but it's one of my favorites. Offer $125 and you'll get a hell of a good pack for a great deal. Another benefit to Craigslist, which is organized by state and town, is convenience. Once I find something it's never far away.
I should also mention the purpose-built sites for outdoor gear, like GearTrade.com. Prices seem comparable to Craigslist, but because it doesn't get much traffic, only a few buyers have high ratings, which makes me a little uneasy. You may also run into selection issues—I couldn't find any canister-type camp stoves, although there were quite a few packs and sleeping bags.
You might also take a look at Mountain Equipment Co-op's Online GearSwap page. MEC act as referee, lending the exchange credibility and providing a safe harbor for buyers and sellers both. You also can find people to hike with! A win all around.