The legal answer to this question is that the vendor cannot rescind the contract and force you to pay the higher price, unless the vendor could prove that the price was so obviously wrong, that you either knew or reasonably should have known of the error. This is legally termed the "doctrine of mistake").
The practical answer, however, is that if you're in China, and the vendor is in the USA, and it refuses to sell at the original price, then you would have to sue in the USA to win your case. Unless you're prepared to fly to the vendor's locale to sue, you cannot prevail. And, since the cost of travel is not part of a damage award granted by a court, your case create a sizable net loss for you.
Consequently, this is one of those times, where the law is undone by geography.
It may be of little solace to you, but I have had the same difficulty with U.S. clients and vendors located in China. It's impossible to win, due to geography and the cost of travel. So, the real lesson here is to try to always buy from local vendors -- so that if there's a problem, you can force them to appear in court to defend their position.
I realize that my answer may not be exactly what you were hoping to read. However, under the circumstances, the best that I can do is to explain what the law is and is not, so that you can avoid expending valuable resources looking for answers that do not exist, and concentrate on the options that are actually available.
I hope I've answered your question. Please let me know if you require further clarification. And, please provide a positive feedback rating for my answer -- otherwise, I receive nothing for my efforts in your behalf.
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