well, the first and most recommended suggestion from me is do not accept bitcointalk accounts as collateral, in most cases you'll get default by the client. and then you'll face problem by selling accounts, as selling account now adays very tricky.
can it be done same way by me changing the passa nd email id for time been to hold his account once paid i can send back all detail
and of course you need to change all details to secure the account. and one more important thing get the sign message publicly.
thank you for providing this information quite helpfull ..yes signing message is publicly ..but when he provide the collateral and member account login detail do i need to get this in signed message if so what is format and this can't be publicly it suppose to me pm ..let em know