I use tech forums, mainly HardOCP, Anandtech, and Xtremesystems. While most of the stuff bought/sold there are tech items, you can find some non-tech goods ther

I use tech forums, mainly HardOCP, Anandtech, and Xtremesystems. While most of the stuff bought/sold there are tech items, you can find some non-tech goods there. You might also have better luck buying/selling niche equipment on niche forums, e.g. headphones on head-fi, AV equipment on AVS forums.