I really don't see the point of the ebay feedback system. It only works one way: buyers can leave negative feedback on sellers, but sellers cannot give negative feedback to buyers. So buyers will only ever have large, positive feedback scores.
As you might have guessed, I have had bad experiences as a seller. In one case, the buyer was either pretending that what I'd sold him didn't work, or was simply technically inept. In another case, having won the buyer decided he didn't want the item after all. Much as I would have loved to give both these deserving people negative feedback, I couldn't.
I think ebay is in an excessively dominant position, allowing them to abuse their market share. The listing fees seem very reasonable, but the final value fees (10% for computer bits, for example) are high. Also, they force you to offer PayPal as a means of accepting payment, which nets them another 3.4% from non-business sellers.
I think I may revert to using postcards in newsagents' windows, and see how I get on! I've successfully sold a couple of things on Gumtree, which seems to have a good following too.