The China of when the stories from the antique roadshow tells and the China of today are two very different things. (Not even counting the thousands of junk pieces that antique roadshow has to go through just to find one piece of show off for tv).  The "antique" items that you can find in the markets are fakes.  Even if you happen to get lucky and stumble across some old man in a shop that actually is selling the real thing (and the hundreds of other people didn't even notice), then you have to be lucky enough to make it out of the country with said antique. For China will claim it as a national treasure.

So don't buy something in the market thinking you'll be rich when you get home.  Buy something that you feel will get a great sourviner and/or gift of your time in China.