It basically comes down to what your role is. If you have control over the building then you can insist. If you are there as a risk assessor then all you can do is make recommendations based on the guides, building regs etc.
The major part of the job is to sell it to the client and the person involved, you need to convince them why it is in their best interest to do whatever is best, turn the desk round or fit a fire alarm in the outer room etc. Bear in mind that even if they do have a vision panel in the door if they haven't been sold the reason next time you come back you will find the panel has been covered by a poster or frosted film, (I don't like people looking in on me) or coats hung over it etc.
In the risk assessment world you have to get used to the idea that you can't make anybody do anything, you must tell them what they need to do to make themselves safe (and cover your own back). But at the end of the day all you can do is warn and then say 'told you'.