Being a KIWI, tipping is so foreign to our way of thinking that for me it is something that would have to be bought up at the time of discussing the hunt price but after the base price was excepted.
Having said that I think Tatume's point is valid. How much and to who needs to understood up front then having a base to work from it would be the actual service given that would determine the amount. I would see it as a GST ( goods and services tax) that would be payed directly to those involved be comfortable with that.

Von Gruff.