With a guy like me in the boat -- talking all the time, hyped up and absolutely frenetic every time he hooks up -- I've had guides offer ME money if I'll just get out early and walk!
My favorite tip came after a phenomenol day -- really once in a lifetime -- on the Zipperlp when my buddy and I had so many hook-ups that we seriously lost count. Between the two of us it was something over 50 and might have been 60, all in the middle of a snowstorm. An absolutley surreal day that had some episodes like buddy Slick's being hooked up and then kicking over the homemade heater (Coke can with gasoline in it), setting the bottom of the jet boat on fire. So there I am in the tip of the bow watching the flames dry out Slick's wet waders mid-thigh while Bob (not THE Bob) is kicking snow over the fire trying to put it out, and Slick is yelling 'Don't let it burn my line!' (That was the only time I actually DID want to get out and walk back but we were about 5 miles above the take-out.)
Anyway, at the end of this Alice-in-Wonderland day we ask Bob the Guide what he wants. He said 'Brad, I need a fishing vest. Yours looks to be too small for you. How 'bout that?' I said 'Sure -- once we're done for the week it's yours'. Now Bob is a very particular steelhead guide as he uses just one method, and it absolutely slays 'em. So because he's such a purist, Slick and I loaded the vest with all sorts of [Bleeeeep!] that you take on fishing trips and never use -- T-Spoons, #25 Flouro pink Hotshots, 8" pink worms, halibut jigs, the whole works -- and dropped it off at his place while Bob was out.
He called us later that night at the lodge and said he that while he unpacked the pockets he was laughing so hard he thought he'd hurt himself.
So what was that worth? I dunno. Maybe $45 for the vest and $10 in miscellaneous junk from the two of us on top of a $300 guide fee.
In Australia (where NO ONE tips) I usually give the guides few 'draft choices' out of my tackle box. Lures are expensive in Oz and I get Christmas cards from Dave Cabela, so it's no BFD replacing some of the American Classics back home.
I don't think there's a point to this tale other than to let the guide know you had a good time, and to put a little dough (or merchandise) in his hand -- 10-15% for an average good day feels about right. Someone rowing a drift boat gets a little more, particluarly if they rowed upstream any to put me in better water for landing a fish.
But the really valuable things about using a guide aren't the fish you catch on the day, it's the techniques you pick up plus the knowledge of where the fish hold under the prevailing conditions.
But those guides who race down the river . . . zilch.