Some great replies here, and bases are already covered. But having read what others have said, I think I wanted to stress something~IF the service was top notch and the guide tried his/her best to get you into fish and give you a great day, then tip accordingly. If you're not 100% sure of that, you be the judge. I've had really good, and really bad experiences with guides and KNOWING HOW TO SET-UP a trip with them is key. Explain clearly what your expectations are. In my case, I always offer a "wish list." I learned this the hard way when fishing with a guide on the Indian River in Florida. Big reds on the fly was the goal, and after hours of fruitless attempts to do so, no hook-ups. So, it occurred to me that there must be other species in there that would be more agreeable, and asked if we could explore a bit. The guide had assumed "reds or nothing" when in fact, the day was saved fishing for snapper, snook and ladyfish.

I could say allot more, but will add only one other point. Guides are people, and you'll run into good ones and bad ones. At the end of the day, you're paying good money for the guide to be at his best. Even if he is not, there should be little evidence of it. Friendly banter is cool, but I don't care to hear about all his/her problems or about how every other guide on the river is an idiot. The best guides are as gracious as they are knowledgeable.