R81 - well said overall. I say overall, because the act of turning your client down could mean losing your job and that puts an enormous amount of pressure on LESSER men/women, I would suggest.
No arguing...being helpful and perhaps directly informative to one or two less worldly wise....
Disclaimer...this advice applies specifically to the UK, although it will apply equally in most other Western jurisdictions.
It is unlikely you would lose your job for doing your job correctly for two reasons:
1. Even in aviation, most people who get to own/run companies are not actually dumb, however much they give the impression that they might be. People who own/run companies are well aware that good staff are - literally - worth their weight in gold and they will look after them as such...even if they don't get along.
2. Assuming your employee has worked for you for two years, if you fire them without good reason, and without following employment protocols, you are bringing a sh1tstorm down on your company. Any employee in the UK that allows themselves to be fired without cause and does not head straight for the nearest employment lawyer is basically ****ing nuts.
For most human beings firing someone is extremely traumatic (trust me...been there, done that). I am an occasional business mentor and one of the commonest failings in business is directors/owners NOT firing people that it is glaringly obvious they should.
So don't be scared of ghosts under the bed...they are usually not there.