Having mostly been on the other side of this when I was younger, guiding is crap work. I could go on about all of the downsides- being away from home, poor pay, long hours, licensing cost, wear and tear on equipment and vehicles, short season, difficult clients, shady outfitters…. it's no way to make a living and most guides don't actually make anything resembling a living. This isn't like the Starbucks machine asking for 25%. Tipping guides is longstanding tradition and without it, most probably lose money on the deal, or at best break even. I don't know why anyone even bothers to do it. if I were a good guide for a hunt and got stiffed you better bet I'm not taking you next time, and a good outfitter isn't going to put you near the top of the list for a future booking. Most outfitters should have suggested gratuity on their web page and that's a good place to start. The best client is the one who is so generous he tips a life changing amount of money.