If the client were viewing existing and finished prints (as in a gallery), they obviously have the choice to buy or not to buy.

However, if the client has approved the images and also viewed examples of your work (not necessarily the exact same image, but sufficient to judge and approve the technical quality of your silver gelatine prints), I think they are rather unreasonable to expect a custom printed order and still have the right to arbitrarily change their mind and reject it. And I can't see the problem in invoicing as originally proposed, especially as you are offering such a generous refund policy.

I also feel that the "art advisor" is not helping and is undervaluing your work.