You can choose your sellers very carefully. Always read and review feedback for any seller you are contemplating transacting with. Make sure the percentage is at least 98.6% positive, and if it's a high volume seller, 99% is even better. The figures quoted above are not "official". Just my opinion as a buyer. Once you've established they have a good percentage, take a look at the actual number of feedback they've received. Make sure they have significant feedback as a seller (not just a buyer), so you know they have a solid track record with a good reputation.
You might find this tool interesting:
http://www.gumshoo.com
When you view an eBay auction using gumshoo, it is automatically scanned for potential auction fraud. If gumshoo finds potential auction fraud risks, they are displayed in the form of an alert.
A very informative link for you:
http://cruentidei.waterhole2.com/ebay/goodbuyer.html