first thing to do is check the sellers feedback
usually I don't bid on items if the seller has low feedback or alot of negatives
ask seller questions before bidding
ask if they give tracking numbers ...I don't bid unless I get tracking numbers...this way I know when my package will be at my door
If buying expensive items ask if they insure the package (because some don't,inurance is important)
If you make a purchase keep all emails paypal reciepts and so on ..this is all your proof of purchase
and this probably isn't the best thing to say but STAY AWAY FROM SELLERS AND BIDDERS Over seas
I have had way too many problems with foreign exchanges
and you can find out where the seller is from on his or her auction page
Everything has its good and bad points ,but
if you use common sense you shouldn't have any problems
I hope you get the chance to experience ebay
I have used it for buying/selling for over 7 years
and i have had very few problems
I have made alot of money and i have got alot of cool things for sometimes less than half the retail price on items that are still in perfect condition