If you have found that thing you want to buy. Make sure you have a good look, ask for more photos or more information.
Make sure you check the sellers feedback - this is very important this will show you if you are going to:
1: get your item
2: Get it in good condition, or what was advertised.
If you are not sure on the seller. Ask questions regarding the product and postage. A good seller will always respond. If they do not respond maybe you should consider not buying that product.
If you do buy a product and do not receive it. Inform ebay at once.
I hope this helps for any questions you may have for buying on ebay.