I have bought 3 times from Ebay, paying online. I buy from them only when the item is not available in the local store, say a Vantec Stealth 92 mm fan. I never buy costly items from them. Make sure that the the dealer had been an ebay seller for a long time, say 2 or 3 years. But generally the prices are very high, sometimes twice the market price.
Anyway every time I got the item prompt and in good condition.