Learning that those silver coins were antique and that they used to be a currency in East Asia, the treasure hunters looked on hungrily. Those sorts of finds were valuable.
However, Li Du had already done a background check. The US trading silver coins were not that valuable. That was because there used to be tons of them, especially after the year 1873.
Following the year 1873, in order to compete for the Far East trade and overtake the Mexican position in the Chinese silver dollar market, Congress had increased the silver content of the coins. Thanks to that, the Americans earned the favor of the Qing dynasty businessmen.
At that time, a massive amount of trading coins was exchanged in the world. Principally, antiques had to be scarce to be valuable. When there were too many of them, the value would decrease.