If a vendor sent their bank details via a signed message in the block chain then a change of bank details could be arranged by sending a new signed message from

If a vendor sent their bank details via a signed message in the block chain then a change of bank details could be arranged by sending a new signed message from the same address with the new details. Obviously it would need to be agreed in advance that this is the method of changing payment details, then the buyer can absolve responsibility to the vendor as it will require the vendor to maintain security of their private key.