If you really enjoy the trip, the guide got you into fish ( or at least you could tell he threw his whole arsenal and heart at it ) and was proffesional and polite and didn't make you feel like a dope... I would tip 1/3 of the cost of the trip, so if he's $150.... $50, may seem like a lot but the guy is teaching as well as serving, I have tipped guides as much as 100% becouse they worked their asses off and were an absolute pleasure to spend the day with. on the other hand, if the guy just sucked and you left feeling cheated.... no reason he shouldn't feel the same way. this is my own personal scale, not an industry standard by any means. I am still close friends with several of the guys Ive fished with, and since have fished with them for free, so a nice tip can lead to a cheaper trip during the slow season or down time.
The tip should have little or nothing to do with the number of fish tagged.
I've tagged fish with rotten guides and offered no tip at the end of the trip. I have tipped big for a guide that, as stated above, put his heart and sole into the trip and came up fish-less. This nice tip, turned into a complimentary trip on one of those "HOT BITE" days that I'll never forget!