Yeah, I have had 2 Hart hvy barreled rifles, a 7mm-08 and a .30 x .378. Both out shoot me. I don't hesitate to use their barrels.
I don't usually shoot a custom rifle
at all. The owners normally want to break in their barrel. I do keep in touch with them to be sure that they are satisfied, though. I agree with Bounty Hunter, very few people are able to pay for the bench time and range time to do load development for them, and most 'smiths don't have the time themselves to provide the service. However, if a customer is not able to make a rifle shoot, then you would have to take it back and make the time. You can't stand to have a rifle out there that won't shoot, no matter what the reason is.
Choose your stock carefully. The finest metal work can't deliver in a crappy stock.
Good shooting, Tom