The entire notion of tipping, or the obligation to tip, is really Helter-Skelter in this country. Guides, waiters, barbers and everyone else who routinely get "tips" should be paid properly for their services. Tipping should not be expected by anyone and a small tip would denote exceptional service.
Why does a guide typically get 10%, a waiter typically gets 20%, while others get a fixed amount. No one tips a bartender based on the cost of cocktails, he gets a few bucks per drink, if you're so inclined.
I've lived in the same house for 40 yrs. I get curbside garbage pick-up. Three times a week all of my garbage and recycling is picked up before I get out of bed. Do the men do an exceptional job that deserves a tip? I don't know, but about 10 yrs ago I found out that many of my neighbors tip the guys. So for the last 10yrs, I give the 3-man crew $100 every Christmas. It makes absolutely no sense to me and maybe I should be tipping other service providers that I haven't thought about. I just try to do the right thing but like I said, "Tipping in this country is Helter-Skelter.