eBay sellers who allow "best offer", but have it set to automatically deny pretty much everything.
I'm one of those people, but if you have ever sold via ebay you will understand why its annoying as heck when someone keeps low balling you with stupid offers so I just get it to decline anything stupidly low :X
Most of the time I see it, it's someone who saw something in pristine condition and all the accessories go for that much or a similar but way more desirable product (think SSK vs Lexmark or Unicomp M) go for that price. Their's, on the other hand, looks like ****, is a different model, or is missing stuff. Then when you point that our, they say the best they can do is $5 under list price
The absolute worst are those who have a make an offer and reject anything less than the BIN price or anything more than $1 under BIN price.
So many eBay sellers are **** though. I had one who had shipping listed as $20.but to wait for a separate shipping invoice (pretty sure that violates TOS). After a week, no invoice, so I paid. They come back pissed that I paid and demanding an additional $20 in shipping. I told them to **** off and ship it or give me refund.