I'm not sure why you would want to tip someone ahead of time? As I understand it, TIPS stands for "To Insure Proper Service" right.... A good reputable guide should be taking you to the best spots regaurdless of a up front tip...

I would wait to see how the hunt goes. If the guide works his tail off, does a good job, is courtous, etc. then I would tip him regaurdless. Obviously more if successful.

It would suck to give the guy $100 up front (or whatever)and then he's a total slacker the whole hunt - wouldn't want to reward that!!