I think it is important to look at some of the responsibilities of a ph.
You are responsible to help the client find an huntable trophy animal.
You must ensure that the client obey the legislation of the area where you are hunting.
You are responsible for the safety of your client your staff and your own safety.

I have never fired any shot at a clients animal up to now, if there are no dangerous game on the property we hunt on, I sometimes do not carry my rifle with me. If I do get a client that is a very bad shot and he wounds an animal and mess up on a second shot, I will definately take out the animal to take him out of his misery. I have seen (I was not the ph but was on the hunt with another client)a hunter fowling up a shot at 20 meters and totally miss on two further chances on the animal, then it is the ph's job to take out the animal. Luckily I have only seen it happen once.

When there are DG on a property I always have my rifle with me. When it comes to the safety of a client, staff or myself I will not hesitate to shoot. As said up to now I never had to take a shot, but if the circumstances require rapid response I will shoot.

The client is paying for the hunt and for his trophy animal, it is his privalage to fire the shots. Backup shots should be discussed in detail before you go into the bush. Clients have asked me to put a backup shot in an animal if it was wounded and he takes his second shot. Up to now it was not needed. There are circumstances where a ph have no choice than to take down an animal, but it must be the exception not the rule.