We highly suggest you do NOT place market orders unless you understand the ramifications of them. We adhere to the SEC definitions of LIMIT and MARKET orders.
http://www.sec.gov/answers/mktord.htm
http://www.sec.gov/answers/limit.htm
If you place one of these orders, we cannot undo what happens. If you have a discrepancy in the amount of coins that you have either sold or received, please verify your order type and ensure that your ordered completely filled.