I've had problems twice on eBay since I've been a member (7 years).
Between the eBay reporting system, PayPal, Square Trade and the Post Master General, I've had no problems resolving them.
Just a casual user of e-Bay - but we have had problems - misrepresented articles, seller backing out after a successful low bid, etc. - about 40% of the time. Have had a number of friends who rave about their 'buys' and know one couple that made a pretty respectable 'living' (@100K/year) selling on eBay stuff they picked up at yard sales.