When I stalked professionally I did NOT expect a tip; I was given a great many bottles though. In the letter I sent people explaining the stalking on offer I made this explicit and that my personal view was that any tip should reflect perceived effort NOT success. If someone did not even see a deer then no outing, or daily, fee was charged at all and if possible I would reset a date with the client for the not too far distant future. I also cut short days, and charged less, when the weather was so atrocious that the client was unable to enjoy it or it was so misty that we would do more harm plowtering about than we would ever see deer. I never advertised my services and usually had more folk wanting stalking than I could provide.
Many years ago, as a youngster, I once only embarrassed myself by over-tipping. I had been fishing for trout on a famous loch due west of Inverness highly successfully. I tipped the retired head-stalker who had ghillied for us (he was also the former RSM of the Lovat Scouts - Willie Fraser) as I would have for a successful stag stalk. He made a special journey to come back later that evening saying I had made a mistake and that it was too much. I explained my reasoning, about his effort and his skill, but the magic of the day had gone. He felt embarrassed and so did I.
To answer the very original question I would say it should always be at the end; be that a day, a few days or a week. Especially if the stalker has also prepared trophies for you, or done other work not usually a part of the day (eg skin an animal etc) then these extras and the tip should all be settled together.
