Yes, getting back to the original question, good idea.
Bakes,
The first client sounds like he is really wanting a good hunt and hopefully also take a quality head if the oportunity arises.
Therefore I would give him my best effort and try to deliver what he is paying to get.
The second client sounds like he is really just wanting to buy a record head to show off and doesn't care much about hunting or ethics etc.
So if hunter No1 takes a good head and the monster head was still available, and this other guy wants to pay what it is worth, I guess I could give him my best effort also to try and deliver what he is paying for.
With true free range hunting there is no guarantee that we will find and get the monster anyway. Some bloody poacher has probably already nailed him if he is really all that good!

Regarding how the trophy fee is paid for the monster head,
only a fool guide would try giving the land owner the shaft!