I use eBay or Amazon for parts, accessories, etc. - items that are small enough to ship without problems. There are a couple of good bike shops that sell via eBay at decent prices and give quick service. But I would rather use CL for items that I want to check out prior to handing over the money. I did buy a mountain bike and a Saris rack on CL and have sold a couple of old Schwinns there.
CL does have some limitations - I am in a major metro area so there is quite a large selection of various "stuff" available to choose from. But if you live out in the boonies or some smaller city, the selection is smaller unless you want to drive some distance to check out an item.