You can still be scammed if the seller is
dishonest, it's just that ebay provides some fraud
protection if you follow their rules and file a
complaint within 90 days of the end of the
auction. A seller with many positive feedbacks
does not guarantee that s/he is trustworthy
because people are less likely to give negative
feedbacks to avoid retaliation. Nevertheless, it
is an available and good indicator, especially
when the seller has hundreds and hundreds of
positives, and few or none negatives.

---Trebuchet