When buying jewelry on eBay, check the period the seller has been a member on eBay, assess his percentage of positive feedback, check the jewelry for markings that verify authenticity, and use a payment method that offers fraud protection. Check shipping charges before bidding, and read the seller's return policy.
Go to the sellers' feedback summary pages to view comments from other buyers, and buy from sellers with extensive and positive feedback. Most credit cards and payment processing services, such as PayPal, offer fraud protection that allows buyers to dispute transactions. Do not pay for items with personal checks or instant wire transfers. Research to find similar items, and gauge the authenticity of the jewelry.