Bargain.sol

// Shortened for brievety
// Message format keccak256 of packed `SellerAddress`,`BuyerAddress`,`ItemAddress`,`ConfirmedValue`
contract Bargain {
    function transferItemWithEthers(address itemAddress, bytes _signedDataByOwner) public payable {

        address itemOwner = Item(itemAddress).owner()

        bytes32 bytes32Message = keccak256(abi.encodePacked(itemOwner, msg.sender, itemAddress, msg.value));
        address recoveredSigner = recover(bytes32Message, _signedDataByOwner);

        require(recoveredSigner == itemOwner, "Not signed by item Owner");

        ItemsRegistry(registry).changeOwnership(itemOwner, msg.sender, itemAddress);

        itemOwner.transfer(msg.value);

        emit OwnershipTransferredWithEthers(itemOwner, msg.sender, itemAddress, msg.value);
    }
}