Some I have come across in my time (protect the buyers out there):
misstazz500: person sold me something claiming it was new, and they just refurbed it. Wouldn't accept return. Ebay customer service and resolution sucked, basically allows sellers to be deadbeats.
rwshelton111: this guy has some sort of memory loss, so don't believe the prices he quotes. Runs a store called Planet Stuff and Things...tells you something already. The guy is also a jerk and abusive in his emails.
Worst part of all this is sellers generally wait untile buyers leave positive feedback, or they will use the feedback as a threat to tarnish your record.
Have met a ton of good sellers online, but Ebay really needs to set up some sort of arbitration such that they can look at all the evidence and negate someone's negative feedback threats. It really needs to be penal to start enforcing a degree of quality on some of these cons out there.