When James Canning-Cooke sold his Volkswagen van to a Russian buyer in is home of Tallinn, Estonia, the deal came with an unexpected condition: The man wanted to pay for the vehicle with bitcoin.

Although the 42-year-old expatriate Englishman's digital-currency holdings have since doubled in value, he now is faced with the challenge of what to do with the 22 bitcoin—currently worth about $18,600, according to Coindesk's index of three bitcoin exchanges.

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