Fishing guides, bartenders, servers, hell even the barber who cuts my hair, any and all professionals that you tip shouldn't be subject to a guaranteed "tip" or even a standard tipping percent.
I'm not one of those people who ALWAYS leaves a 15% tip. Before you think I'm some cranky d!ck who's stingy on tipping, I'm actually a fairly generous tipper and usually tip 20% or up for good service.
However, when I get sh!tty service, be it at a restaurant or from a fishing guide, I have no problem giving little to no tip. If someone half asses their work or doesn't give 2 schits about me or makes my experience less than pleasurable, then the hell with giving them 15% or even 5%. On the flip side, if my guide or waiter is great, makes it a memorable day on the water or if the service was great and I enjoyed my time at their restaurant because of them, I'll tip them well and tell em they made me experience special.
Fortunately, most people in service related industries are for the most part pretty good folk and I don't have too many bad experience. If you do a $hitty job you shouldn't get tipped, nor should you expect to get tipped. If you are that person, you have the wrong perception on how things work and need to be told so. Vice versa, if you have a guide who's bending over backwards for you and making your day a most memorable one, tip the help and tell him he did a great job....