Agreed, and thats why I laid it out as I did. But even in the world of high dollar parts, one is not always willing to "guarantee satisfaction" with parts supplied by others. The fault of a poorly shooting (or underperforming) rifle would always toggle between the gunsmiths work, and parts not supplied by him. This discounts shooter ability, components, etc. It will always be a source of contention, if there is ANY problem down the road.
Anyone is willing to stand by a product or job, if supplying the major source of problems.
NOT everyone will do so if working with purchases out of his control.
It's only human nature, and with the amount of people having work done, this will show up more and more. And let's face it, a lot of todays customers accept only perfection, at least from others. Example: Pay attention in a restaurant, to those that are always dissatisfied with food or service, usually the same ones with "problems" at auto service, gunsmith or other.