If it sounds to good to be true, it likely is. Even sellers with great feedback can be scammers.
For example:
I bought a new GPS unit on ebay. Price was about 30% under retail, seller had good feedback though so I went for it. Got the unit and it was genuine and good. Weird thing was that it came from Tiger Direct with a invoice for full retail price.
About a month later I get a call from Tiger Direct accusing me of using a stolen credit card. Turns out this guy was listing items for great prices on ebay, then when somebody bought one, he would buy it with a stolen credit card form Tiger or Newegg and drop ship it to you. People get what they wanted, and so leave positive feedback, only to find out months later how the guy was offering such good prices. This guy got reported and shut down by ebay, problem is he can just come back under a different ID.
Sellers can get ripped off to.
My sister once tried to sell a laptop on ebay. Soon she got an e-mail from a buyer in Nigeria offering her 3x her asking price. She said OK, I'll ship it when I see the money. Then she get's an e-mail from "Paypal" saying that she had received payment, but that Paypal couldn't release it to her account till the item was shipped and received. I explained to her that Paypal does not work that way... ever.
Turns out it was a phony Paypal e-mail, directing you to a phony Paypal site. She logged into the real Paypal to find no payment at all. She reported buyer to ebay and they where shut down. I only hope they didn't scam to many people out of their laptops and stuff.
Moral = Be very careful when using ebay, I'd bet 95% of ebayers are honest, but there are always the few out to scam you.