I have noticed that gamers were often very gullible. They expect so much from the GM in terms of adventure hooks that they are ready to 'bite' at the first opportunity. Myself included :)
I have hence thought of listing here a few ideas for confidence tricks in which the PCs are the 'marks' (victims of the con scheme). Unfortunately, I haven't devised any of these — if I had, I would be now living in some remote villa on the Mediterranean coast, and not in snow-covered Paris — they are from the Wikipedia.
I won't re-write the contents of the Wikipedia article, just jot down a few ideas to make them fit into a TCE game.
In Imperial China, mines were usually government-owned property, and only the government (or its subcontractors) could engage in the trade of metals, salts, etc. As a consequence, no sane person would ever buy a mine from a con artist.
However, rich collectors or traders could be interested in a piece of land with rare herbs or medicinal plants. 'Salting' the piece of land would simply involve planting the rare vegetable and then pretend it is native to the area.
There are many possible ideas for this particular con scheme. Here is one, that would particularly fit in a Qīng-era game. The con artist approaches the PCs and explains them that a British opium smuggler has been jailed in Canton; the Lǎowài is to have his head cut off in two weeks' time. His relatives are immensely wealthy and are ready to pay a huge sum to get him out of prison and save his life. However, it will take more than two weeks to get the money from India, where they reside. In the meanwhile, the PCs should pay the necessary bribe to the warders; they will be returned ten times its amount as soon as the ship with the money arrives.
Romances usually do not play a major role in role-playing games (alas). It will be hence difficult for the GM to involve any one of his players in such a con scheme, unless the latter like their PCs to go to brothels, tea houses, etc., There, they could meet a prostitute who promises one of the PCs that he could marry her if only he could buy back her freedom. This could go on and on as new hurdles would always appear.
Fortune Telling Fraud
Fortune-tellers were numerous in Imperial China, of all classes and persuasions (see TCE, p49-55). As with the Romance Scam, there is little probability the PCs would spontaneously consult a fortune-teller. Here's an interesting variant, however: the PCs find a precious ancient sword in a treasure. Somehow, a con artist disguised as a fortune-teller (or even a genuine fortune-teller) cons the PCs into believing that the sword is cursed and must be destroyed. The rest is as per the Wikipedia article.
This can be hilariously played upon unsuspecting gamers. The nicer the PCs, the better. One of the PCs could be a travelling healer, intent on curing people afflicted by some natural or magical malady. Or a monster hunter, looking for a Hànbá or similar disaster-bringing creature. In one of the villages where the party stops, a woman feigns to be afflicted by the illness the PCs are trying to remove. She invites the healer/monster hunter in her home, and undresses to show her wounds. At that exact moment, the angry brothers and male cousins of the female con artist suddenly come in. The 'mark' is then forced into marrying the woman.