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Due to the prohibition of exchanges in China, over-the-counter trading (https://en.bitcoinwiki.org/wiki/Over-the-counter) has flourished there.
Traders used the fact that Chinese investors were left without an opportunity to buy cryptocurrencies at an exchange. What they did was buy Bitcoin, Ethereum et al abroad and sold them over-the- counter (OTC) in China for a high mark-up.
Lately, the margin has diminished since more people tried to exploit this arbitrage opportunity (https://news.bitcoin.com/bitcoin-mules-flood-china-as-otc-cryptocurrency-trading-flourishes/)