when I owned a bike shop, I fully expected my clients wouldn't know how to overhaul their suspension fork, maintain their drivetrain or bleed their brakes and would always charge to do those things for them. I always offered a limited time service to cover the break in period, where it's expected that things will need adjusting, at no extra cost.
Personally, I think it devalues the expert's expertise to provide anything 'for free'. Nothing's free, everything costs someone something.
I haven't been making knives long enough to have much to add to this conversation by way of personal experience, but I am starting to think that the only service I will ever provide 'for free' would be warranty service, ie; failures that I unknowingly built into my work.
If someone wants me to sharpen a knife I made, I don't think it's unreasonable to charge a fee- just enough to remind that person that what I do is not something that they can do, which is why they bought the knife from me to begin with. I think it actually adds value when you charge for a service which you are an expert in. People don't often value things very much which they receive for free.
