Sodastream Gas Exchange £18.98 (£8.98 after deposit refund) @ Sodastream

What the OP has not said is this code is issued when you register a new soda stream to your account so you can easily get it legitimately by registering your soda stream if it's not been registered before.

Due to the above there is the possibility of cancelled orders when they realise it's being abused but I doubt that will happen.

It is also once per an account which is why, if you get a message it's been used this might be why.