Ebay is a great place to get wonderful deals on jewelry.  The retail market is so highly marked up that you can get quality items for a fraction of the price.  Check the feedback on sellers.  Beware of any sellers that do not have high ratings or are altogether new to Ebay. 

Jewelry is a very emotional item, so comparison shop.  I "watch" items in My Ebay.  That way you can check activity and the current bids.  It also allows you to compare items.  You also do not waste your time bidding on items that are outside of your price parameters.  Read the listing in detail.  Some items are damaged or heavily worn. Don't discount these if you have a fair jeweler who can do repairs and set stones.  Also in the listing look for the quality of the merchandise.  Is it solid gold ?  Are the stones natural?  If it is not stated as "stamped 14K", or natural, it probably isn't. Can a ring be sized?  Plated metals, and some designs that are inlayed or the settings wrap around the band, can not be sized.   Diamonds have a rating for color and clarity as well.  Smaller stones are less valuable, so the total carat weight can be deceiving.  Frequently the total carat weight reflects the less precious stones as well as the diamonds.

When buying chains and bracelets, look at the total gram weight, the lenght, and the clasp.   

If you are considering a laboratory created gem, the russians make the best.  These do not have the same value as a natural stone, but you can't beat the "BLING". 

When you find a seller that you like, visit their store.  Chances are they will have other items that you are interested in. 

Remember that gemstones and gold can be good investments, gold is currently about $600/gm and climbing, plus you get to enjoy them as well. 

Regarding shipping:  There are many sellers who offer a discount if you buy more than one item.  You will probably have to email them so they can amend you invoice to reflect the discount.

Jewelry makes great gifts and alot of sellers include gift wrapping.  Don't be a last minute shopper for the hoildays.  Shop early, avoid the insanity of mall shopping between Thanksgiving and Christmas.