Both Ebay and Craigslist are full of sellers who either have no idea
what stuff is worth or are fishing for suckers. But there are still
deals to be had (as a buyer) on both. You have to take time to keep
trolling.

I've used both a lot and the short version is -- Ebay is best for
selling stuff that's not too hard to ship. All you need are 2 people in
the world who want it and you get best price. Craigslist is best for
selling stuff that's hard to ship, but you can't be greedy if you
really want to get it out of your garage. Ebay is great for buying
weird things that not everyone wants (like 3-phase motors). Craigslist
is good for buying higher ticket or big items (with high shipping cost)
because you don't pay until you see it and like it.