Only a legal professional can offer legal advice and Buy Bitcoin Worldwide offers no such advice with respect to the contents of its website. To sell 10 bitcoins you must have deposited 10 BTC to your account with the exchange. Local Bitcoins facilitates some of the aspects of the trade. Remember that the bitcoin exchange and the bitcoin wallet are not the same things. There are only 21 million Bitcoin, and as time goes on, they become harder and harder to mine.