* @return A {@code CoinbaseTransfer} representing the buy.
* @throws IOException
*/
public CoinbaseTransfer buyAndAgreeBTCAmountVaries(final BigDecimal quantity) throws IOException {
final CoinbaseTransfer buyTransfer = coinbase.buy(quantity.toPlainString(), true, exchangeSpecification.getApiKey(), signatureCreator, getNonce());
return handleResponse(buyTransfer);
}