First off, my expertise are in Chinese and South East Asian Ceramics and note jade or sculpture. But I think the same advice can be applied here.
eBay is a great place to buy antiques IF you know what you are doing. If you don't know your stuff, you will most likey end up purchasing a fake. I would dare say 90% of asian antiques on eBay are fakes. The good side is the prices for the real items are much lower there. However the real jewel of eBay is the volume of sellers. There are a huge number of sellers that get their items from estate sales, garage sales and grandma's old attic. You will be surprised to find the number of treasures being offered by sellers that have no idea of the true value or importance of the item. These items are sold wrongly described and in the wrong catagory. If you look hard enough and have patience, you will always find that hidden treasure. I have already purchased a number of Ming period blue and white ceramic items for dirt cheap this way including many Qing items.
Back to you. Just because something is old does not mean it must be expensive. Construction sites throughout China are constantly unearthing relics of the past. It is very typical to unearth bricks dating to the Han period. As a consequences, such relics are flooding the market. There are a number of eBay sellers that specilize in selling large volumes of these small relics. They are not worth very much but interesting to have. They mostly consists of old coins, beads, bronze trinkets, ceramics bowls and even some small jade items. Generally these can be purchased from $10-$20.
Remember that certificates of authencity do NOT mean a thing! Anyone with a printer can make their own. The same goes for sellers that claim that their piece have been authenthicated by so and so expert or museum. There is NO WAY you can certify this at all. It's you against the word of the seller. And there are a lot of con artists out there. To be fair, there are also a small number of trust worthy sellers that sell real stuff. A simple rule is that the more outlandish looking, magnificant looking antique is most likely not an antique at all.
Knowledge is power. If you plan on being a serious collector or scholar or even purchase as an investment, you have to get reference books to read. A general rule is to reserve about 10% of your collecting budget to purchase books. Old auction catalogues are also a good source of important information. There is no way around it. It's easier to authenticate ceramics as you can inspect the color, the paste, the glaze etc... But with jade it is VERY difficult. It seems the one way is to examine the shape and decorative element. Decorative styles change over time. A Song dragon will differ from a Ming dragon which would differ from a Qing dragon. If you can identify such differences, you are far better off. If not, you have just only touched the very tip of a large iceburg :P
Welcome the the word of Asian antiquities, it will consume you and be a life long achievement to pass down to the next generation. I will help you any way I can about ebay and sellers etc... contact me if you wish. Just don't ask me how to authenthicate jade. I don't have a clue.
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