Don't buy from sellers in China! I don't know about the Straits Settlement coins but Trade Dollars are widely counterfeited. To be honest I would be much more comfortable buying items like these from an established coin dealer, eBay is just too swamped with fakes and as you say, they tend to generate a bidding frenzy so you probably end up paying more.
Non illegitimis carborundum est. Excellent advice for all coins.
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