SellerMismatchError and SellerNotFoundError has status code 500 when it should have 4xx

[civsiv]

When making a C1 call, I received a 500 status code for a SellerMismatchError. I am unsure where this is defined in the specification but it should not be a 500. I would guess that it should be a 400 Bad Request, but at the very least it should be 4xx

[nickevansuk]

Note this also applies to SellerNotFoundError

[nickevansuk]

Also applies to OrderAlreadyExistsError and OrderProposalVersionOutdatedError which should be 409s. The 500s in the spec, except for subclasses of InternalOpenBookingError , should be reviewed should see if they should in fact be 4xx errors.