Shanghai street hawkers (those who sell merchandise on a freelance basis on the streets of Shanghai) can be quite troublesome — especially on Nanjing Road, around the Yu Gardens area, and sometimes along the Bund. There are other places where hawkers tend to gather but these are the most common places where they accost tourists.
Nanjing Road is notorious for the “shirt, watch, purse, DVD you want?” sellers who quickly unfold pieces of laminated paper showing the knock-off products they peddle for quick cash. If you decide to follow one of these people to their shops be aware that it may be far away from where you met them. What they are selling are illegal, fake copies of real brands. Some countries will block these items from entering the country. France, for example, will confiscate French brand name rip-offs it finds them in your suitcases at the airport, according to rumors from French who travel to and from China frequently. Also be aware that there are some dangers associated with following a stranger promising to sell you a fake item. He may lead you into a trap of some sort or a con, though physical harm is unlikely.
Your best bet is to memorize and repeat the phrase “bu yao,” which is pronounced “boo -yao” and means “don’t want.” This you need to say in an abrupt fashion in order to get the tones accurate. Say both words in a downward tone so that both sound like commands, this is the closest approximation to the correct tonal pronunciation of the words “don’t want.”