Well, it's been a awkward time, and I'd like to have your opinions as pro luthiers. A new customer brought his old 100$ (maybe less) classical guitar with terrible plastic nut and saddle. He asks for a improvement so he can tune with no headache. I make him a new bone nut and bone saddle without changing strings because he doesn't want to spend much money on it. Here come the troubles.
He tries it and find an annoying noise on the strings, while tuning ability is good now. Well listening carefully and plucking in a particular way, there's a tiny little noise. Not a fret buzz, nor rattling or sitar like sound. A bit like a free winding on a string or something similar. Changing strings does not improve situation, shimming the saddle or double checking my nut slots' shape neither. I spent an hour on it trying a lot of things, checking for loose braces, etc.. with no success.
When he comes back, he tries it, tell me that the guitar is not working at all because of these little noises, and that it did not have this problem when he walked in my shop the first time (unfortunatly I can't confirm this, and it's part of the lesson I guess). So to his eyes I'm not good enough and guilty for these noises.
I told him I spent a lot of time on it, and did all I can, but that I did not find the problem's origin. So I charge him half the price of a new nut and saddle and give him the address of another luthier in town who is only building classical guitars for maybe 30 years (I only do this for 7 years as a full time job).
Customer's not happy but what else could I do? It's the first time I have a dissatisfied customer of this kind, and it really is a pain. What would have you done in my place?