I haven't tipped my farier with money, but I certainly tell him how very much we appreciate the quality of his work, his ability to handle horses and his unfailing promptness. He's the only horse shoer we've ever had who always arrives on time.
My daughter, the domestic diva, has baked him pies as a thank you and I have given him an enlargement of a cute photo of his daughter - she was squatted baby fashion at a vet check examining rocks.