ebay: auctions suck, bidding on stuff isn't my idea of fun. There is too much of negative press surrounding fraud etc, so you have to go out of your way to portray yourself as not being a criminal. craigslist: people are cheap, it is handled face to face, if you are selling something large, usually random strangers come into your house.

So that really has nothing to do with coding, but those are my gripes with each.