One that I'm sure most people will agree with me on is
Wheeljackslab. In my experience, it's not that he is a shady businesman, but he has no concept of customer etiquete. He once sent me an email, but his address was not clearly written in the email (instead, he had put a link to his page, where the address was written, with the instructions "Do not send payment for ebay items to this address," or something like that), so I asked him where to send the money. Instead of writing a few lines down (God forbid he'd do something for a confused customer), he decided to argue with me, saying that he had sent it. The only reason I ended up giving him good feedback was that I was having a bad day when I got the package, and it cheered me up. That was only the second time I dealt with him, but it was the last.
Feedback:
http://cgi2.ebay.com/aw-cgi/eBayISAPI.d ... eljackslab
A really unreliable one is
decepticonzero. He doesn't respond to emails for months, then contacts you out of the blue with some lame excuse as to why he was late. The first time, it was because he had a broken finger, so I felt bad, and decided to go with him again, but the next time, the excuse was that he works out of town, so he couldn't keep track. If you're gonna be flaky, you shouldn't sell on ebay.
Feedback:
http://cgi2.ebay.com/aw-cgi/eBayISAPI.d ... pticonzero
The other two I'd warn you of are no longer users anyway. It's been so long since I dealt with these people that I no longer have a reference auction for them.