I do most of my buying on Craig's list. Occasionally I will buy from eBay, but my LBS has a pretty amazing selection of C&V parts, generally at eBay prices, it's a lot quicker and I can check out the part before I buy (The mechanic also has his own collection, so if the shop doesn't have something, I might be able to get it from him directly). I've only sold on this forum. Generally I'll donate what I don't want/need, especially when I buy a donor bike, to the Silicon Valley Bike Exchange. There's a forum member that does a lot of builds for them and he is happy to get the parts.