If it's o.k. with ya'll, being a custom gunsmith, I'll reply to this as well...
Most of us are a funny lot, and I can say that because I know a lot of other custom smiths. The really good ones, as you might imagine, take a LOT of pride in our work. And typically we charge for it also. Now we may have a few friends that we do cut rates or favors for from time to time but that, as a general rule, is an exception and often desired to be kept quiet because we can't have everyone out there thinking we are such nice guys! HA!
Over the years I have received a number of very nice things from my client friends. Most of them know that I enjoy a nice smoke out of my tobacco pipes. And every once in a while, an appreciating customer will send me a tin or two of my favorite Peterson's University Flake. It is always a surprise, and never expected but certainly enjoyed. There have been clients that have given me boxes of cigars, beer, bourbon, nice pipes, t-shirts, hats, and other gifts of appreciation. I even had a guy at Camp Perry insist that I take some money for fixing his doubling pistol before he would leave the trailer, and he just wouldn't take no for an answer. What I've come to realize for myself, and I'm not speaking for other smiths here mind you, is that some people just really want you to know how much they appreciate what you did for them, and their way of showing that appreciation is by giving you something they think you will enjoy...and that's cool...not expected, but cool.
All that being said, the best praise someone like myself gets, in my opinion, is hearing about how good your gun shoots from others. It is always a thrill to get a call or e-mail telling me that so and so won this match or that match with one of my guns. Or that they had the time of their lives shooting a buddies gun that was built here. And that is how guys like me stay in business. Treat folks right, communicate, give more than is asked, and people come back time and again, and they send their friends.
So, do you have to take your smith something he may like for a job well done? No. Should you? Not necessarily. But if you do choose to do it, make it something that when he looks at it or enjoys it, reminds him of how much you appreciated what he did and how much he enjoyed doing it for you. Case in point, hanging on my wall in the shop above my bench is a matted framed picture sent to me of a gun I built for a gentleman that carries the gun everyday on duty somewhere...he sent me that picture...and it reminds me to say a prayer for him each day...things like that...well, they are worth far more than money. And that's my two cents from the point of view of a custom smith.