seller's feedback. If he/she doesn't have many sales with 98% favorable, or better, feedback, you need to be very cautious.
With that said, the main problem with eBay is that people frequently bid more than an item is worth. You need to know the value.
hmmm... I am a skeptic, I know this. But if I could get a camera for less than list??? hmmmm
What do you all think?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic