Ref the transfer- if it a transfer from his account to yours then no it cannot be reversed, only way it can if he could prove that it he didn't do it, fraud etc.... a fast transfer is in essence 'cleared' funds. Just make sure it's a transfer and not a cheque paid in at a branch, stolen cheque paid into your account pretending to be you, quick call to your online banking will confirm how it's been paid in, transfer, over the counter etc....