Agree, do not use credit card details - freelancer is a terrible organisation when it comes to finances - they just debit your card at will, no warning, no opportunity to review the transaction, no notification of the charge - you just find out once you get your bank statement.
Be very, very wary of this company - not saying their dodgy, BUT they are very devious when it comes to transactions.
I think their motto is - "debit any time, just don't tell them and they wont complain"