When searching for jewellery in eBay it is a great idea to search the description and not to just rely on the items title heading.
For example this title: CRYSTAL EARRINGS. Check that they are not glass 'crystal' (which means in the bead world: clear, very shiny and reflective). If they are true crystals the buyer should describe them as perhaps Swarovski crystal or Austrian etc. If you are not sure, contact the seller and ask! They should be helpful in any questions you wish to have answered.
Note whether the item is Silver or stirling silver necklace. Again, check the description. If it does not specify whether they are silver plated, stirling silver etc, then they probably aren't. Again, ask the seller for a more elaborate description. This also goes for gold and any material you are interested in.
Remember also that too many questions to a seller is still not enough. If you are in a retail store enquiring about a piece of jewellery you would probably ask at least a couple of questions before you decide whether you will purchase. Because you don't have the item in front of your eyes, you will probably want to have more assurance of the item...so ask, ask, ask away! The seller should be again helpful if they want the sale.
When you have purchased an item of jewellery on eBay, or anything really, and you are unhappy about the purchase once it has arrived, it is strongly advised that you contact the seller FIRST before leaving negative feedback. This is a common courtesy for both you of you to resolve any issues and the opportunity for the seller to redeem themselves and their product. Most occasions the seller will bend over backwards to keep their positive feedback score to the maximum.
Hope this helps!