eBay has the responsibility to educate not only the sellers but also the buyers especially on how to avoid being defrauded from buying on eBay. Most of the buyers who were defrauded by some frauds actually have the ways to minimize to the risks of being defrauded to the lowest level.

1. Study the feedbacks of the sellers especially these from the buyers. Pay special attention to the negative feedbacks of the seller, which can tell you partially what problems this seller had with his buyers in the transaction. Also try to learn who and for what item left the positive feedbacks. This will tell you the secrets.
2. Try to ask seller the technical questions about the items he is selling, normally a real seller will give you full and correct information about the products in a short time.
3. Try to have the seller's contact and contact him first by email or by phone. Even you have won the auction, you should never pay for the seller prior to your contact with the seller. Normally a real seller is willing and happy to give you his telephone number (Attention: No Mobile). Aslo this will be an important clue for the potential frauds.
4. Try to learn if the seller has a verified Paypal account, or any third-party verifications.
5. Try to learn if the items are covered by Ebay or Paypal or any third-party buyer protections.
6. Try to ask the seller some reference contacts who bought from him before. This is also very important. If a seller has sold something, he should have the record of the buyer's contact.
7. Never use some unsafe payment terms.
8. Study the price of an item if it's brand new. If it's reidiculously much lower than the normal price on Ebay, take care, as NO seller can sell without a basic profit. Some items for promotional purpose are exceptions.

The above can not give you a 100% safety but can be possible methods to minimize the risks to the lowest level.

May it be helpful for your purchasing online.
Good Luck.